Benefits of wheeling economy energy in Canada: quantification and sensitivity analysis

E. Vaahedi, MSc, PhD, CEng, FlEE R.J. Poirier, BSc, PEng C. Necsulescu, DEng, PEng A.N. Karas, BSc, CAM, PEng

Indexing terms: Wheeling, Economy energy, System operation

~

Abstract: The paper describes the studies carried out by the National Energy Board to quantify potential wheeling benefits as part of its review of possible measures for enhancing transmission access in Canada. Computer simulations were per- formed on a planning time horizon to determine potential benefits from bilateral exchanges of economy energy and the additional benefits which could result from various wheeling arrangements. The simulations modelled the interconnected power systems of eastern Canada and the neigh- bouring American utilities which make up the Northeast Power Coordinating Council. From these simulations, the potential benefits for each system involved as well as the net potential bene- fits were determined. The CPU time for the simu- lations ranged from 14 h to 46 h on a VAX 8200 minicomputer. Sensitivity analyses were also per- formed to establish the sensitivity of the results to some operational assumptions and parameters used in the studies.

1 Introduction

The National Energy Board (NEB) was requested by the Minister of Energy, Mines and Resources of Canada to carry out a review to identify measures that could be taken to improve cooperation among Canadian utilities and to enhance transmission access. To identify measures for enhancing transmission access in Canada, two pro- jects were initiated:

(a) a study of technical issues associated with wheel- ing; and

(b) quantification of potential wheeling benefits in Canada. The first project examined technical and economic diffi- culties associated with wheeling and methods to alleviate these difficulties. The second project, the subject of this paper, used computer simulation to quantify some of the potential benefits of wheeling in Canada. This work identifies how important an issue wheeling could be in the Canadian context.

0 IEE, 1994 Paper 146OC (P9), received 31st May 1994 The authors are with the Electric Power Branch of the National Energy Board, 31 1-6 Avenue S.W., Calgary, Alberta, Canada T2P 3H2 Dr. Vaabedi is now with B.C. Hydro, 6911 Southpoint Drive, Burnaby, B.C., Canada V3N 4 x 8

IEE Proc.-Gener. Transm. Distrib., Vol. 141, No. 6, November 1994

Computer simulations were performed on a planning time horizon using real system data to compare alternat- ive operation modes, with and without wheeling. These simulations modelled the interconnected power systems of eastern Canada and the neighbouring American systems. Based on these simulations, the potential bene- fits of wheeling economy energy for each system involved as well as the net potential benefits were determined.

The NEBS CANEBEXS program [I], a sophisticated computer program which simulates system operation, identifies the optimal economy energy transactions among power systems in a network, with or without wheeling, and calculates the associated benefits was used in this project. This program has the following features:

(a) calculation of hourly loads in each system; (b) economic dispatch of available generation in each

system to meet the hourly loads; (c) simulation of the transfer capability between

systems ; (d) simulation of scheduled exchanges between

systems; and (e) identification of optimal economy transactions

using a brokerage method [2, 111.

CANEBEX5 repeats the economic dispatch of system generation in each hour of the study period. In this way, forced outages of thermal and large hydro units are simu- lated on an hour-by-hour basis. This simulation uses a Monte Carlo method to determine whether the unit will undergo a forced outage and, if so, to establish its length in hours. A unit undergoing a forced outage will not be used again by the program until that number of hours has elapsed. Forced outages of peaking hydro and pumped storage units are not simulated. Also, CANEBEXS permits scheduled outages of each thermal and large hydro unit which can be used to simulate annual maintenance outages.

CANEBEXS deals only with operating costs of gener- ation. Capital costs of generation and transmission, whether existing at the start of the study or added during the study period, are not considered. Energy exchanges are made strictly on an economic basis. The brokerage system replaces the highest cost generation in service in the network by the lowest cost generation available for service but not required to meet load. CANEBEXS calcu- lates gross benefits for each transaction by subtracting the incremental cost of the seller from the avoided cost of the buyer. The gross benefits are then divided between the buyer and seller in any proportion desired. These net benefits are then reduced by wheeling charges paid out,

585

where applicable. For the studies in this paper, benefits from were divided equally between buyer and seller.

CANEBEXS allows the user to determine which systems in the network may exchange energy. Trans- actions between systems may occur in either direction or both directions. This feature allows the modelling of high-voltage direct-current interconnections such as those between Quebec and its neighbouring systems. The program has a number of mechanisms for dealing with wheeling charges for transactions between systems which are not adjacent. The user may decide that there will be no charge or apply any one of the following three rate systems: unit cost or ‘postage stamp’, percent of avoided cost, and percent of gross benefits. Wheeling charges may be paid by the buying or selling system and paid up to three intervening systems.

2 Applications

From the beginning it was realised that it would be impractical to simulate all of the power systems in Canada together with neighbouring US systems owing to the computing time and storage requirements, data prep- aration time and the need for a computer program capable of simulating all the systems involved simultan- eously. The approach used was first to model a manage- able part of the Canadian system as a whole and then to study smaller parts of the same network. The results offer a good indication of the total potential wheeling opportunities in Canada. The present study will be extended to other parts of Canada in the future.

It was decided to perform three case studies: one general study of the interconnected system of the North- east Power Coordinating Council (NPCC) of the North American Electric Reliability Council (NERC) and two other studies dealing with parts of the system in more detail. In geographical terms NPCC includes the Cana- dian provinces of Quebec, Ontario, New Brunswick and Nova Scotia and the New England region and New York State in the USA. The general study modelled all the NPCC systems in detail. For the Canadian Maritime systems an equivalent system had to be used because CANEBEXS can only handle up to five systems. The other two studies concentrated on local effects, dealing with wheeling from Quebec and Nova Scotia to Prince Edward Island and from Quebec to New Zealand, both through New Brunswick.

In Canada, only the major utility in each province was modelled. In the United States, all utilities in New England and New York which report to NERC were rep- resented. The individual utilities or pools modelled for the study are as follows.

(a) In Canada the following were modelled: Hydro- Quebec (Quebec), New Brunswick Power (New Brunswick), Nova Scotia Power Corporation (Nova Scotia), Maritime Electric Power Company Limited (PEI), Ontario Hydro (Ontario).

The island of Newfoundland was not represented since it does not form part of the interconnected system. However, Newfoundland’s Churchill Falls hydro plant, in Labrador, was included with the generation in Quebec’s system. PEI, although not a member of NPCC, was included because it obtains much of its electricity from member utilities, primarily New Brunswick.

(b) In the United States the following were modelled: New England Power Pool (New England), New York Power Pool (New York).

586

2.1 System data used in the studies In addition to data on network interconnections, the fol- lowing data files were prepared for each utility or pool.

(a) Load data files. Annual peak loads were based on the latest forecasts from the utilities involved. Load shapes were based on information from the utilities or from Board files. The load shapes were adjusted so that the annual energy demand for each system would corres- pond to NERC forecasts [4].

(b) Firm purchases and sales data files. All known scheduled transactions were included in the files.

(c) Plant data files. Data files include all existing gener- ation plus additions expected during the study period.

All data files were updated specifically for this study. Data files are updated every two or three years to keep abreast of the latest utility plans. The data used to update the files were obtained from various publications and correspondence with utilities (4-10).

2.2 Procedures for studies To identify the benefits of economy changes and wheel- ing, the following procedure was used in all three case studies.

Step I: Simulate the operation of the study network with only prescheduled purchases and sales in place and determine the amount and cost of thermal generation.

Step 2: Repeat Step 1, letting the program identify all the bilateral economy exchanges which can take place, with the associated benefits, and determine the resulting amount and cost of thermal generation.

Step 3: Repeat Step 1, letting the program identify all the bilateral economy exchanges that can take place as well as the transactions which require wheeling to com- plete, with the associated benefits, and determine the resulting amount and cost of thermal generation. This step was repeated for each of the various wheeling scen- arios studied.

By comparing the results of Steps 1, 2 and 3 the benefits of bilateral economy exchanges and the additional bene- fits from wheeling were identified.

2.3 Study No. 1 : NPCC general study The purpose of this study was to identify the potential benefits of wheeling economy energy among the major systems in NPCC. It, therefore, concentrated on opportunities existing among these major systems under normal operating conditions, and left the examination of special situations to the other studies. The study network, as shown in Fig. 4, contained five systems; Ontario, Quebec, New England, New York and MARPOOL, the equivalent system combining New Brunswick, Nova Scotia and PEI.

The following three scenarios were examined: (a) Ontario wheeling: to New England through New

York, and to MARPOOL through New York and New England;

(b) MARPOOL wheeling: to New York through New England, and to Ontario through New England and New York; and

(c) Scenarios (a) and (b) together in addition to: New York wheeling to MARPOOL through New England, and New England wheeling to Ontario through New York.

In carrying out the studies, the process described in Section 2.2 was followed. Thus the following five cases were studied:

Case I. Only committed firm transactions;

IEE Proc.-Gener. Transm. Distrib., Vol. 141, No. 6, November 1994

Case 2. Optimised bilateral economy transactions on

Case 3. ODtimised wheeling scenario ‘a’ on top of top of Case 1;

- Case 2;

Case 4. Outimised wheeling scenario ‘b’ on toD of - Case 2; and

Case 5. Optimised wheeling scanerio ‘c’ on top of Case 2.

The results of these studies are examined in the following Section.

2.3.7 Results: Fig. 1 shows the total network benefits resulting from optimal economy energy exchanges for dif-

year1 year2 year3 year6 year5

Fig. 1 rn Bilateral ffl All trans mt On1 wh Mar wh

ferent wheeling arrangements as well as the benefits for bilateral exchanges only. Benefits in this context may be considered as the saving in fuel costs adjusted to consider the effect of an assigned value of incremental cost, referred to as imputed lambda, for exports of hydraulic energy, which are made in this study exclusively by Quebec. Fig. 1 shows that the total network benefits from economy energy exchanges can increase by about 6% when wheeling takes place compared to the value realised when wheeling is not permitted. This translates into about $21.0 million for year 1 and $36.0 million for year 5. (Fuel costs used in the studies were in Canadian dollars adjusted to exclude the effect of inflation. Assuming a real annual growth rate of 2%, the benefits for year 5 amount to approximately $33.3 million in 1990 dollars.) Fig. 1 also shows that the majority of the wheel- ing benefits can be captured by allowing only Ontario to wheel as compared to the all transactions case.

Figs. 2 and 3 show the total thermal energy generated in the network, and the associated cost, for differing

Network benefts for different wheeling arrangements

7000, I

.. year1 yeor2 year3 year4 year5

Fig. 2 Network thermal generation costs for diflerent wheeling arrangements H Noeconomy 0 Bilateral All trans am Ontwh Mar wh

wheeling arrangements as well as the case where no economy cxchanges takeplace (only scheduled purchases and sales) and that in which only bilateral exchanges take place. These values, which are also good indicators for

IEE Proc.-Gener. Tmnsm. Distrib., Vol. 141, No. 6, November I994

network economic eficiency, show that wheeling reduces the amount of overall thermal generation and the corre- sponding cost. These figures also indicate that the main

4 0 0 , I I I

yeor 1 year2 year3 year6 year5

Fig. 3 Network thermal generation for different wheeling arrange-

Noeconomy 0 Bilateral All trans Ont wh tZi Mar wh IWnfS

reduction in thermal generation occurs when bilateral economy exchanges, without wheeling, are allowed. In effect, the total network thermal generation is reduced by about 16.72 TW h/year when economy transactions takes place. The corresponding decrease in fuel cost is approx- imately $873 million/year. The total network thermal generation does not change noticeably for different wheeling arrangements. In effect, less expensive thermal generation displaces the more expensive when different wheeling arrangements are allowed.

Fig. 4 shows the total economy energy exchanges in the network for the first year of the study for the case

Fig. 4 Year 1990, Case 2: Bilateral exchanges

Annual economy energy exchanges (CW h)

involving only bilateral exchanges (Case 2). Fig. 5 gives corresponding information for the case where all possible wheeling transactions are permitted (Case 5). It shows the actual annual energy exchanges between the systems in the network as well as the net energy flow over each system interconnection. Fig. 6 shows the change in energy transfers between systems when wheeling is allowed. This figure shows that the major changes consist of energy from Ontario displacing New England‘s own generation and its purchases from MARPOOL and, in addition, energy from MARPOOL replacing New York’s own generation and its purchases from Ontario. Fig. 7, which gives weekly average energy quantities wheeled between systems, bears out this conclusion and emphas- ises the effect of wheeling in the study network.

Fig. 8 shows the number of hours in which transfer capacities of different interfaces in the network restricted possible transactions for the case where only bilateral exchanges were permitted. Fig. 9 provides corresponding information for the case where all transactions are per- mitted. These figures show that some interfaces, on average, limited possible economy energy flow in 6OOO h

587

out of a year. Also, the number of hours in which the interconnection limits restrict economy exchanges increases when wheeling takes place and that the north-

0

igi_ 80 70

8 60 & 50 6 40

f 30 -

~ ~-

20 ~

10 0 ~

b

Fig. 5 Year 1990, Case 5 : All transactions a Annual economy energy exchange b Resulting energy flows

Annual economy energy exchanges (GW h)

Fig. 7 Year 1990, Case 5 : All transactions

Weekly average energy wheeled

high voltage transmission systems of Quebec and New England are not interconnected (Quebec supplies New England through facilities isolated from its own system), and

(b) wheeling to PE1 through the New Brunswick system from Quebec and/or Nova Scotia (Study Network 3 of Fig. 10).

These studies confirmed the main findings of the general NPCC study reported in detail in this paper. The wheel- ing benefits, however, vary from case to case depending on the particular systems involved. Numerical results of these studies are not included in this paper.

2.5 Sensitivity analysis In preparing data files for the studies, assumptions were made regardless of the value of some system parameters and operational modes which would normally be selected by experienced engineers and operators in the utilities. These assumptions influenced and controlled the amount of economy exchanges between utilities in the studies. To

5000

4000

3000

g 2000

& $ 1000

i o c VI

-1000

-2000

-3000 Ont -Que Ont-NE Que-Ont Que-NE MAR-Ont MAR-NY NE-MAR NV-Ont NY-MAR

Ont-MAR Ont-NY Que-MAR Que-NV MAR-NE NE-Ont NE-NY NY-Que NY-NE

Fig. 6 All transactions against bilateral exchanges

Change in energy transfers between systems in network when wheeling permiffed

south interconnections are the transmission links more establish how the results obtained were affected by these prone to producing bottle-necks. assumptions, sensitivity analyses were performed. Most

of these analyses were carried out using Study Network 2.4 Other studies 3, however, the analysis involving a system operation Studies were carried out to identify wheeling benefits in assumption, the case of Quebec wheeling to New the following specific cases: England, was carried out using Study Network 2. These

small networks were used because the studies involved New Brunswick (Study Network 2 of Fig. 10) when the much less computing time than those involving the

(a) wheeling from Quebec to New England through

588 IEE ProcGener. Transm. Distrib., Vol. 141, No. 6 , November 1994

NPCC network. The impacts of the following assump- tions and parameters on system benefits were examined:

(a) the incremental cost (imputed lambda) assigned to hydraulic energy exports from Quebec (while this feature of the program applies to all systems in the network, only Quebec exports hydraulic energy in these studies);

assigned an incremental cost of 20 mills/kW h. This assigned cost, referred to in CANEBEX5 as imputed lambda, is used by the program in arranging energy exchanges and calculating benefits in place of the real incremental cost. The actual incremental cost of hydrau- lic generation is significantly less than this value.

7000 I

6000

5000

LOO0 E 0 r

3000

2000

1000

n ” . Ont-Que Ont-NY Que-On! Que-MAR Que-NE Que-NY NE-MAR NE-NY NY-Que NY-NE

Fig. 8 Bilateral transactions only

Year I Year2 Year 3 Year4 Year 5

Numher oJhours in which exchanges were limited by transfer capacity

(b) the difference in system incremental costs (deadband) below which economy transactions are not permitted ;

(c) the wheeling rate; ( d ) system operation; and (e) the simulation initial condition.

The results obtained with the variation of these param- eters are discussed in the following Sections.

2.5.1 The impacr of Quebec’s impured lambda: In the studies carried out, Quebec’s hydraulic energy was

However, it reflects very closely the value of hydraulic generation in day-to-day system operation.

To identify the impact of imputed lambda on the study results, a series of runs was performed with differ- ent values for a case in which wheeling takes place only from Quebec to PE1 in Study Network 3 of Fig. 10.

Network benefits for imputed lambda values from 10 to 25 mills/kW h are given in Fig. 11. As shown in the figure the system benefits increase as the imputed lambda value reduces. Since the calculation of benefits is based on the difference between the buyer’s incremental cost and Quebec’s imputed lambda, benefits will increase as

Ont-Que Ont-NY Que-On! Que-MAR Que-NE Que-NY NE-MAR NE-NY NY-Que NY-NE

Fig. 9 All transactions permitted

Numher o/hours in which exchanges were limited by transfer capacity

Year I Year2 Year3 m Year4 E2 Year5

IEE Proc.-Gener. Transm. Disfrib., Vol. 141, No. 6 , Notiemher 1994 589

imputed lambda decreases even if the amount of energy involved does not change. To determine the effect of changing imputed lambda on the quantity of energy exchanged, further investigation is necessary.

Island I ' by I Scotlo

network

Fig. 10 Networks for other studies

cn ""

50

E! % 40 E

,,$ 30

C

e

- a 5 20 n

10

0 network HQ PE1 NB

Fig. 11 H IO mills 0 IS mills 20 mills H 25 mills

Impact ofimputed lambda on system and network benefits

Fig. 12 shows the network thermal generation costs for different values of imputed lambda. This figure shows that the total thermal generation remains constant for

500

2 400 E

300

C

U) I g 200

100

0 year 1 year2 year3 year4 year5

Fig. 12 COSfS

H I O mills Kl I S mills 0 20 mllls Ej 25 mills

Impact of imputed lambda on network thermal generation

imputed lambda from 10 to 20 and, therefore, the total incurred cost from the network point of view remains constant. This shows that increasing imputed lambda from zero to 20 does not affect the displacement of thermal energy by hydraulic energy. For imputed lambda of 25 and larger, the total thermal energy cost increases indicating that the displacement of thermal generation with hydraulic energy is reduced. It should be noted that changing imputed lambda alters the distribution of profits from a transaction because, the higher the cost for hydraulic energy, the more profit Quebec receives per unit of energy sold when the additional revenue associ-

590

ated with the difference between imputed lambda and actual incurred cost is considered.

2.5.2 The impact of incremental cost deadband: In the studies carried out, a value of 2 mills/kW h was selected as the difference between system incremental costs or deadband below which no transaction would take place. A set of runs was made for the case of Quebec wheeling to PE1 in which the deadband was vaned from 2 to 8 mills/kW m.

The variation of network and individual system bene- fits from these runs is shown in Fig. 13. This figure indi-

30

25 C

g 20 E 3 15 + ... $ 10 01 n

5

0 network HQ PE I NB

Impact of deadband on system and network benefits Fig. 13 H 2 mills 0 4 mills 6 mills 8 mills

cates that the benefits do not change significantly for values of deadband between 2 and 6 mills/kW h. However, the benefits decrease significantly for values of 8 and more. Further detailed assessment in this case revealed that, above a certain deadband, hydraulic exports are displaced by cheaper thermal energy.

2.5.3 The impact of wheeling rates: In the studies carried out, the wheeling rate was set at 20% of the avoided cost associated with the transaction, paid by the seller. This value was modified to assess the impact of the rate selected on the benefits realised.

Fig. 14 gives the incremental system benefits, adjusted for wheeling charges paid and received, resulting from

2 15 c - 1

g o ? 0 5 "-

- 0 5 1

yeorl year2

Fig. 14 Benefits from wheeling WC = 20% of avoided cost paid by Quebec €3 HQ @ NB PE1 H System

wheeling. This figure was obtained by subtracting the benefits obtained for the economy case (bilateral trans- actions only) from the benefits obtained for the case involving wheeling from Quebec to PEL The figure shows that PEI's benefits surpass the total interconnected system benefits indicating that the assumed wheeling rate would not result in a fair distribution of benefits among the parties involved. Fig. 15 portrays corresponding results except that the wheeling rate has been reduced to 10%. With this wheeling rate in effect, New Brunswick

IEE Proc.-Gew. Transm. Distrib., Vol. I41, No. 6, November 1994

would be better off not to wheel. Fig. 16 shows the bene- fits for a wheeling rate of 20% with Quebec and PE1 each paying half. With this rate in effect, PE1 gets the greater

3 2 5

15

E 05

A -05 -I

-1 5 -2

5 2 - 2 1 e o

yearl year2 year3 year4 year5

Fig. 15 Benefitsfrom wheeling W C = 10% avoided cost pard by Quebec

Quebec NB BII PE1 W Network

16 ,

1 -4

1.2 C g 1 E 0 8

Ui 06

- ._ e

% 0 4

A 0 2

0 - 0 2 1 I I I

yearl year2 year3 year4 year5

Fig. 16 Benefitsfrom wheeling WC = 20% avoided cost split between Quebec and PE1

Quebec NB rm PE1 W Network

part of the wheeling benefits whereas Quebec and New Brunswick would be slightly better off over the study period than if they had performed only bilateral exchanges. Fig. 17 shows the benefits when the wheeling

-1- L A yearl year2 year3 year4

~ year 5

Fig. 17 Benefitsfrom wheeling W C = 20% avoided cost paid by PE1

Quebec 0 NB a PE1 W Network

rate is 20%, paid by PEL This figure shows that PE1 would be worse off and Quebec would get most of the wheeling benefits.

Figs. 14-17 show that the choice of wheeling rate affects the distribution of the wheeling benefits signifi- cantly. To promote wheeling, one important consider- ation is to provide a financial incentive for all the utilities involved by proper distribution of the benefits. Sensitivity studies of the particular situation similar to those per- formed here can assist in deriving a wheeling rate which will accomplish this objective.

It is important to note that the study described here assumed that all economically feasible transactions within the transmission capacity of the system intercon-

I E E Proc.-Gener. Transm. Distrib., Vol. 141, No. 6, November 1994

nections would take place and calculated wheeling charges and benefits accordingly. However, in real life conditions there are a host of other factors, economic, technical and institutional, which must be considered in developing a wheeling policy in addition to the setting of the wheeling rate.

The NEB recognised the importance of such issues and, as mentioned in the Section 1, initiated a separate study dealing with technical and economic issues associ- ated with wheeling and possible methods of alleviating them. Based on this work, the NEB developed a number of principles which should be considered when dealing with wheeling including the ones given below.

(a) The utility providing wheeling services (the wheeler) should be compensated for direct costs (including any benefits foregone because of the service) plus a reasonable share of the net savings.

(b) Reliability of service to the wheeler’s own cus- tomers should not be affected by providing the service.

(c) The wheeler must make the ultimate decision relat- ive to the use of his facilities

(d) The wheeling utility should plan, design and operate its system so that, while providing wheeling ser- vices, it meets its regional and interregional obligations at all times.

2.5.4 System operation: There are cases where major operational assumptions need to be made. One of these assumptions was made in Study 2 involving Quebec wheeling to New England through New Brunswick. Quebec can supply firm power to New England directly from its grid or from isolated generation facilities. Fig. 18

300

- 250 , I l

yearl year2 year3 year4 year5

Fig. 18 operational modes W radial supply H wheeled

Total benefrtsfrom economy energy transactions for different

gives the benefits obtained from economy energy exchanges for these two possible operational modes. In this case, the benefits almost double when a direct link exists between the Quebec and New England systems via New Brunswick (wheeled) as compared with the case when Quebec supplies the New England system from iso- lated facilities (radial). These results show that if, in order to ensure reliability of service, a utility is required to supply firm power to another utility from isolated gener- ation, its benefits from economy exchanges could be reduced significantly.

2.5.5 Impact of the random number generation process: In the simulations made, a number referred to as the seed was selected to start the Monte Carlo random number generation process used in determining gener- ating unit forces outages. Selection of the seeds, which may be any four-digit numbers between 0 and 1, was entirely random. The Monte Carlo simulation process is determined by this seed. A different seed would produce a

59 1

different simulation. It is important to note that the bene- fits quoted in this paper are based on only one of many possible simulations. As energy exchanges and the corres- ponding benefits are affected by generating unit forced outages which would be different for simulations with dif- ferent seeds, additional simulations with different seeds would be required to determine the most likely value of benefits.

Ten studies were performed simulating wheeling from Quebec to PE1 for a one-year period using different seeds. Fig. 19 compares the benefits for the 10 different random processes. This figure shows that the total system benefits have an expected value of $29.66 million with a standard deviation of 2.5%. Fig. 20 shows the cumulative distribution of benefits for the studies. This figure gives the probability that the benefits would be less than a certain value. For example, as the stepped curve shows, the probability that the benefits would be less than $30.2 million is 80%. A normal distribution was used to approximate the probability distribution of the benefits. The resulting approximated cumulative distribution, also shown in Fig. 20, indicates a close agreement between the real results (stepped curve) and the approximated normal distribution.

35 r

1 2 3 4 5 6 7 8 9 10 scenorto

Fig. 19 Impact offorced outage simulation on benefits

-- 7 , 0.8}

0.2/ -/’ beneflls, $ m d l m

Fig. 20 ~ real distribution ~ ~ _ _ approximated normal distribution

Cumulative probability distribution of benefits

2.6 Computer requirements The above network studies were performed on a VAX 8200 minicomputer. The main parameters determining the study’s CPU time are:

(a) number of power systems; (b) number of thermal and large hydraulic generating

units in each power system; and (c) the study period.

CPU requirements for a five-year simulation as shown in Table 1 varied from 14 h to 46 h depending on the network studied.

592

Table 1 : Computer requirements for various case studies

Study Number of Total number of thermal CPU time description systems and large hydro units h:m:s

Study 1 5 544 46 :34:43 Study 2 3 327 17: 12:24 Studv 3 4 271 14: 02 :42

3 Conclusions

In considering the results of the studies it should be remembered that these results are dependant on the load forecast and generation expansion plan assumed for each utility. The results of such studies may be considered to have a statistical uncertainty similar to that in the utility plans used to prepare the data.

The studies carried out lead to the following conclu- sions.

The total economy exchange benefits for the NPCC network amounts to about $3 billion for the study period of five years. This includes benefits from both bilateral exchanges and wheeling.

The wheeling benefits vary with the case study and time. However, on average, the above studies show that when economy energy exchanges that require wheeling are allowed system benefits increase by about 6-10%.

In the studies, wheeling increases system benefits by 6-10% above the value realised when all bilateral economy exchanges possible between neighbouring systems are carried out. If, in real life, full advantage can not be taken of these exchanges, then wheeling would allow other economy exchanges to take place. Therefore, it can be stated that wheeling of economy exchanges offers at least an additional 6-10% in benefits and it could make possible economy exchanges which might have been impossible without it. The reasons for not making bilateral exchanges could be operational, polit- ical etc.

In the studies, the major constraint to economy exchanges was interconnection transfer capacity limits. In addition, in all the cases studied, the number of hours that the transfer limits restricted the possible economy exchanges increased when wheeling takes place.

If, to ensure reliability of supply, a utility is required to supply firm power to another utility from isolated gener- ation, its benefits from economy exchanges could be reduced significantly. The Quebec-New England case study showed that the benefits from economy exchanges almost double when a direct link exists between the Quebec and New England systems as compared with the case when Quebec supplies New England from isolated facilities.

The distribution of wheeling benefits among the util- ities involved is a balancing act which could create incen- tives for wheeling. In each instance where wheeling is considered, studies could be carried out to identify the most suitable wheeling rates so that all the parties involved come out as winners.

The value assigned to the incremental cost of hydrau- lic resources could affect the total network benefits. The selection of this value should be based on studies so that under no condition would local thermal resources dis- place imported hydraulic resources.

The deadband within which no economy dealing should be performed seems to be dependent on the study systems. It is possible to find a reasonable deadband which reduces the number of transactions while only affecting the benefits slightly.

IEE Proc.-Gener. Tronsm. Distrib., Vol. 141, No. 6, November 1994

The sensitivity of benefits to the starting point of the 4 ‘1989 electricity supply and demand‘, North American Electric Reli-

Monte Carlo simulation is low, having a standard devi- $:$:yo-:’: ~ ~ ~ ~ ~ o p m e n t Plan, 1989-1991 ation of about 2.5%. 6 Correspondence with Ontario Hydro 1987,1988 7 ‘Acid =as emissions derived from the Canadian utilities simulation

4 References -

code for the Provmce of Ontano’ Monserco Limited report, 1989 8 US Deuortment ofEnerqy’s Electric Power Monthly, 1989, (12),

1 RAU, N.s., and NESCULESCU, c,: ‘A for energy exchanges in interconnected power systems’, IEEE Trans. Power Syst., 1989,4, (4, pp. 114771153

2 COHEN, L.: ‘A spot market for electricity - Preliminary analysis of Florida energy broker’, Rand Note, N-1817-DOE, 1982

3 ‘IEEE reliability test systems’, IEEE T ~ ~ ~ ~ . , 1979, p s ~ , (61, pp, 2047-2054

9 ‘Nucle& - New York- Power Pool’s Electric Power look ahead,

10 Correspondence with NB Power and Nova Scotia Power Corpora-

11 DOTY, K.W., and McENTIRE, P.L.: ‘An analysis of electric power brokerage (2), pp. 389-396 systems’, IEEE Trans. Power Appor. Syst., 1982 PASIOI,

1988-2004’, 1988

19”

IEE Proc.-Gener. Transm. Distrib., Vol. 141, No. 6, November 1994 593