TECHNICAL NOTE Distribution Automation Division PRTN-0003B, 11/00 Page 1 of 12 Siemens Power Transmission & Distribution Inc. Distribution Automation Division P.O. Box 29503 ! Raleigh, NC 27626-0503 Tel: (800) 347-6659 ! Fax: (919) 365-2552 ! [email protected]s Relay Settings for the 7UT51 Differential Protection Relay 1.0 Introduction .......................................................................................................... 1 2.0 7UT51 Relay Configuration and Settings ............................................................. 1 Application Example.................................................................................................... 2 2.1 Relay Configuration.............................................................................................. 3 2.2 Insert Transformer Data ....................................................................................... 4 2.3 Setting the Differential Function (87) .................................................................... 5 2.4 Setting the Overcurrent Protection (50HS and 50/51) .......................................... 8 2.5 Setting Output Contacts and Targets ................................................................... 9 3.0 Conclusion ......................................................................................................... 10 4.0 References ........................................................................................................ 12 1.0 Introduction The following paper is a discussion on the setting of the 7UT512/3 Differential Relay, and consists of a simple example and various hints on how to implement settings on the 7UT512 relay. The 7UT512 require all its settings in per unit values, all rated to the nominal current of the transformer. This requires conversion for any settings performed in primary or secondary values. All the relay setting are explained in detail in the relay instruction manual but this paper can be used as a supplement to assist in the interpretation of the relay settings. To simplify the settings process, this paper will only discuss the setting of the Differential (87) and Over Current (50/51) functions. 2.0 7UT51 Relay Configuration and Settings Follow the order of the actions below to ensure that the relay is setup up correctly and in the least amount of time. 1. Configuration of the relay for an application. 2. Insert the transformer data. 3. Setting the differential protection (87& 87HS). 4. Setting the overcurrent protection (50HS & 50/51) 5. Marshalling of the settings to output contacts and targets.
Transcript
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1.0 IntroductionThe following paper is a discussion on the setting of the 7UT512/3 Differential Relay,and consists of a simple example and various hints on how to implement settings on the7UT512 relay.The 7UT512 require all its settings in per unit values, all rated to the nominal current ofthe transformer. This requires conversion for any settings performed in primary orsecondary values. All the relay setting are explained in detail in the relay instructionmanual but this paper can be used as a supplement to assist in the interpretation of therelay settings. To simplify the settings process, this paper will only discuss the setting ofthe Differential (87) and Over Current (50/51) functions.
2.0 7UT51 Relay Configuration and SettingsFollow the order of the actions below to ensure that the relay is setup up correctly andin the least amount of time.
1. Configuration of the relay for an application.2. Insert the transformer data.3. Setting the differential protection (87& 87HS).4. Setting the overcurrent protection (50HS & 50/51)5. Marshalling of the settings to output contacts and targets.
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Figure 1 depicts an example that will be used to implement the settings to be applied tothe 7UT512.For transformer protection, the differential protection (87) must be set to 20% of nominalcurrent of the transformer, and the instantaneous overcurrent protection (50HS) must beset to trip at 4000A in 50ms. To protect against high load currents and through faults, theinverse time element (51) must remove the transformer from the network in 10 secondsfor a current of 800A. The actual settings for both the 50HS and the 51 elements areentered in per unit values, rated to the nominal current of the transformer, not in CTsecondary values. The application requires that the transformer protection (the 87 and50HS) trips the HV and LV breakers, while the transformer load protection trips only theLV breaker.`
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2.1 Relay Configuration
The relay must first be configured to the application example. The example belowshows the Device Options, address group 7800, under the configuration of the 7UT512relay. The best method to understand these device options is to open a relay file in theDIGSI software and configure the relay for the intended application. This paper will notdiscuss the other settings under the configuration heading (7100, 7200 & 7400) . Thesettings contained in these address groups can normally be applied in their default stateand are set during the commissioning period to set up the relay communications andfault recording options.By configuring the relay first, all protection functions that are set to be nonexistent willnot appear if the setting and marshalling menus.
Configuration7800 DEVICE OPTIONS7801 Selection of the protected object 2-winding trans7816 87-State of the differential protection EXISTENT7821 Backup overcurrent protection Reference side 1
87
50/51
W 1
W 2
7UT512
600 / 5
9.4 MVA13.8 kV / 2.4 kV
Z=6%
3000 / 5
I HV prim.
I HV sec.
I LV prim.
I HV sec.
Figure 1: Transformer Application Example
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7824 49-Thermal overload protection 1 NONEXISTENT7825 49-Thermal overload protection 2 NONEXISTENT7830 State of external trip function 1 NONEXISTENT7831 State of external trip function 2 NONEXISTENT7885 Select settings group NONEXISTENT7899 Rated Frequency Line Freq of 60 Hz
The settings above ensure the setting 7821 is set to the correct reference side of thetransformer. In the example the overcurrent function is required on the HV side of thetransformer.(Comment: ANSI standards recommend a separate overcurrent relay on theHV side for transformer protection. Otherwise, loss of the differential relay results in aloss of main and backup protection for the HV side). There is only one overcurrentelement available in the 7UT51 relay, and this element can be used on either winding ofthe transformer, HV or LV. Set 7816 to the relay reference side 1 if the relay primarywinding is connected to the transformer HV winding. Check all wiring against theconnection diagrams in the 7UT51 Instruction Manual on Page 186 for the 7UT512relay, and Page 184 for the 7UT513 relay.
2.2 Insert Transformer DataThe relay uses transformer data to ensure the correct calculation of the differential andrestraint quantities. The relay does not require auxiliary transformers to match thesecondary currents to the transformer primary currents. These settings are entered intothe relay under address block 1100. This address block is found under the Settings tabin DIGSI.Printed settings from DIGSI:1100 TRANSFORMER DATA1102 Rated voltage of transformer winding 1 13.8 kV1103 Rated apparent power (VA) of winding 1 9.4 MVA1104 Rated primary current of winding 1 CT 600 A1105 Starpoint formation of winding 1 CT Towards transformer1106 Processing of winding 1 zero sequence current Io-elimination1121 Vector group associated with winding 2 0 *30°1122 Rated voltage of transformer winding 2 2.4 kV1123 Rated apparent power (VA) of winding 2 9.4 MVA1124 Rated primary current of winding 2 CT 3000 A1125 Starpoint formation of winding 2 CT Towards transformer1126 Processing of winding 2 zero sequence current Io-eliminationThe relay uses the settings 1102, 1103, 1104, 1122, 1123 and 1124 to calculate thesecondary currents seen by the relay. The relay also needs to calculate the phaseangles of the current seen by the relay. This is done using settings 1105, 1125, and1121. The example in Figure 1 shows that the star point of CT’s are connected suchthat the star point grounding is facing the transformer. Set 1105 and 1125 to “Towardstransformer”. If the transformer star points are grounded 1106 and 1126 must be set to
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“Io-elimination”. If the starpoint is not grounded 1106 or 1126 can be set to “WITHOUT”.If you are not sure about the grounding condition of a transformer winding set 1106 and1126 to “Io-elimination”, as this setting works under all circumstances.
Figure 1 also shows that the transformer is a delta-delta connected transformer, with nophase shift between the transformer windings. Setting 1121 indicates the connectiontype of Winding 2, and the phase shift between the reference winding (Winding 1) andWinding 2. Table 4.1 on page 46 of the 7UT51 Instruction Manual lists the settings for adelta connected reference winding. For the example shown in Figure 1, a delta-deltaconnected transformer with no phase shift, the proper setting is for address 1121 is 0.
2.3 Setting the Differential Function (87)The relay has a considerable amount of settings for the differential function, found inDIGSI under group address 1600. For most applications, no settings which need to bechanged. The default settings are based on long experience with numerical transformerdifferential relays, and cover nearly every standard application.. However, these settingscan be used to alter the relay characteristic curve if necessary. This could be required ifa tapchanger has a high regulation range (> +15%, -15%), which is effectively a linearCT-error. Other settings can also be used to set the relay response to inrush current.These setting should remain at default values unless there are information available tojustify a setting change.
Printed settings from DIGSI:
1600 87-TRANSFORMER DIFF PROTECTION DATA1601 87-State of differential protection ON1603 87-Pick-Up value of diff protection 0.20I/In Trans1604 87HS-Highset Pick-up RMS value of diff prot. 7.5 I/In Trans1606 87-Slope 1 of operating characteristic 0.251607 87-Base point for slope 2 of operating char. 2.5 I/In Trans1608 87-Slope 2 of operating characteristic 0.501610 87-State of 2nd harmonic restraint ON1611 87-2nd harm content in the different. current 15 %1612 87-Time for cross-blocking with 2nd harmonic 0 *1 Cycle1613 87-Choice a further (n-th) harmonic restr 5th harmonic1614 87- n-th harmonic content in the diff. current 80 %1615 87-Activ time for cross-blocking w/ n-th harm 0 *1 Cycle1616 87-Limit IDIFFmax of n-th harmonic restraint 1.5 I/In Trans1617 87-Max. blocking time at CT saturation 8 *1 Cycle1618 87-Min. restr. current for blocking @CT satur. 5.00 I/In Trans1625 87-Trip time delay of diff. current stage 0.00 s1626 87-Op time of high-set diff. curr stage 0.00 s1627 87-Reset dly after diff op has been initiated 0.10 s
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Setting 1601 must be set to “ON”.Setting 1603 is set in per unit values and is thus set to 0.20 for a requested setting of20%. For the HV-side, where the nominal current of the transformer is 393 A, this leadsto a sensitivity of 78 A.Calculating the maximum differential current that can be caused by tap changer errors, ,can be used to check the setting. The relay is connected to a C200 CT in the example.This CT has a ratio error of not more than 3% between 1 to 20 times of the secondarycurrent if the secondary burden does not exceed 2 ohms. Therefore, the maximumdifferential current produced by the CT’s if the errors between the LV and HV CT’s areopposing is 3% + 3% = 6% under nominal conditions If the transformer has a tapchanger the setting must be increased by 1% for every 1% of tap the changing range.For a setting of 20% the setting must be increased to 30% for a 10% tap change range.So for the example in Figure 1, the required setting of 20% is adequate, because there isno tap changer at the transformer.The setting 1604 is set to a level where a fundamental differential quantity of thismagnitude can only be an internal fault. Above this setting the differential relay will issuea trip regardless of the second harmonic setting in 1611. Set this to 7.5 and the relayoperates high speed when the fundamental differential current is higher than 7.5.It can be shown, that the fundamental quantity of an inrush is never higher than half ofthe peak value of the inrush current. Therefore the factory setting covers inrush peakvalues up to 15 times of nominal current. Inrush peak currents of this magnitude havenever been seen in fault records.Setting 1618 is used by the relay to activate the Through Fault Restraint Area. Thisfeature is used to consider the effect of CT saturation on the differential relay. Thisadded security ensures that the relay will not trip under high through fault conditionswhen CT saturation is more likely to occur. Relays without this feature must increase thesecond slope (parameter 1608), thereby desensitizing the relay for some faultconditions. The default setting is 7 but we have found that a setting of 5 is moreappropriate. The application note Increasing the Security of Low Impedance DifferentialProtection in Reference [3] describes the relay differential algorithm in greater detail.Settings 1625 and 1626 set the delay times for the 87HS and 87 functions. Thesesettings are normally set to the minimum setting of zero, or no intentional time delay.The following calculations must be done to ensure that the correct CT taps have beenused.First calculate the transformer HV primary full load current.
AV
SprimHVI 27.3933108.13
104.93 3
6
=××
×=×
=
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Calculate the transformer HV secondary full load current. This is also the relay nominalcurrent referred to the protected object, the transformer.
AHVCT
primHVCTprimHVIHVI 28.35
60027.393sec
sec =÷=÷=
Calculate the transformer LV primary full load current.
AV
SprimLVI 29.22613104.2
104.93 3
6
=××
×=×
=
Calculate the transformer LV secondary full load current. This is also the relay nominalcurrent referred to the protected object, the transformer.
ALVCT
primLVCTprimLVILVI 77.35
300029.2261sec
sec =÷=÷=
Now calculate the ratio between the rated transformer primary current, and the rated CTprimary current, for each transformer winding.
Winding 1 65.0600393 ===
primCTIprimHVIRatio
Winding 2 75.030002261 ===
primCTIprimLVIRatio
Note: The ratios of the rated primary current to the rated CT primary current must bebetween 0.25 and 4.00 for each winding. These ratios are always based on themaximum rated power set at addresses 1103 and 1126. This is important, as thiseffects the accuracy of the differential and restraint calculations.
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2.4 Setting the Overcurrent Protection (50HS and 50/51)The overcurrent feature of this relay consist of a high set overcurrent function(50HS) anda normal overcurrent function that can be configured to a 50 or a 51 function dependingon the selection of setting 2111. These settings are rated to the nominal current of thewinding, which is the value of I HV primary calculated previously.
Printed settings from DIGSI:
2100 OVERCURRENT PROTECTION ( DTL / IDMTL )2101 State of back-up overcurrent protection ON2103 50HS-Phase highset (Def. Time) O/C pickup 10.16 I/In(_transformer)2104 50HS-Delay time for 50HS ( Def. Time) funct 0.05 s2111 PH O/C time characteristic Very Inverse2112 50T - Phase (Def. Time) overcurrent pick-up 2.00 I/In(transformer)2113 50T - Delay time for 50T (Def Time) funct 1.40 s2114 51 - Phase (Inv. Time) overcurrent pick-up 2.03 I/In2115 51 - Phase inverse overcurrent time dial 1.51 s2116 Phase current measurement format Without Harmonics2118 Reset delay after trip has been initiated 0.10 s2121 Phase overcurrent stage effective :Manual cl Inactive
Calculation of setting 2103.The example requires a pickup value of 4000A primary, which is converted to per unit onthe nominal rating of the transformer winding by either of the following methods:
17.1027.393
4000400050
16.1028.35
6004000secsec
50
===
=÷
÷=÷
÷=
primHVIHS
OR
HVIHVCT
primHVCTprimHVIHS
The delay time for 50HS 2104 must be set to 0.05 s as requested.In order to set address 2114 it will be required to convert 800A to a per unit value thatcorresponds to a multiple of the full load current. We can then use this value to select acurve in address 2111 and time multiplier according the required 10 s delay.Calculate for address 1114.
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03.227.393
80080051
03.228.35
600800secsec
51
===
=÷
÷=÷
÷=
primHVI
OR
HVIHVCT
primHVCTprimHVI
For address 2111 select the curve that is suitable for the application so that itcoordinates with the downstream protection relays. The curves are found in the 7UT51Instruction Manual (Reference [3]) on Pages 103 to 105. For the example we selected avery inverse curve.To set the time dial setting 2115 use the curves on Page 104 Figure 8 to select thecorrect value. The time dial selected is 1.5 for a 10s delay at a current of 2.03 times thefull load current or 800 A primary.This setting can also be calculated by using the formula shown on Page 104 for a veryinverse curve. Please note that I/Ip is the multiples of the Pickup current and that is thesame value that was calculated for address 2114. (51)
51.148258.0
103.2138.19
10
48258.01/
138.19
0.2
0.2
=
+
−
=
+
−
=
TD
IpI
tTD
The settings for the definite time stage (50T) are not used, as these settings 2112 and2113 are disabled when a curve is selected under address 2111. These settings areonly active when address 2111 is set to definite time. If 2111 is selected to definite timethe settings for the 51 function 2114 and 2115 are disabled.Setting 2116 is normally set to “Without Harmonics”, so the relay acts on thefundamental 60Hz current only. If the transformer feeds a rectifier for a steel smelterwhere harmonics are generated or any other transformer that is likely to see harmonicsset this setting to “With Harmonics”.
2.5 Setting Output Contacts and TargetsRelay marshalling sets the functions or events that control all output contacts and targetLEDs. The first step before attempting to marshal the required functions to the outputsor inputs is to clear all the default marshalling from the relay. Set all the output contacts,
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discrete inputs, and LED’s to “No Function Assigned”. After clearing the defaultconfiguration, marshal the required functions to the intended relays. The examplerequires two contacts to be marshalled to trip the HV and LV breakers respectively.Start by marshalling the contact that will be responsible to trip the HV breaker. Thiscontact only opens the HV breaker for trips issued by the 50HS function and the 87function.
DIGSI marshalling example.6401 Configuration of Trip Relay 1 001 5691 87 -Diff protection: Trip 002 5692 87HS -Diff protection: Trip 003 2441 BU 50HS -Highset O/C time expired 004 0001 No function assigned 005 0001 No function assigned 006 0001 No function assigned 007 0001 No function assigned
Marshall the contact that will be responsible to trip the LV breaker. This contact mustopen the LV breaker for trips issued by the 87, 50HS and 51 functions.DIGSI marshalling example.6402 Configuration of Trip Relay 2 001 5691 87 -Diff protection: Trip 002 5692 87HS -Diff protection: Trip 003 2442 BU 50/51 -Overcurrent timer expired 004 2441 BU 50HS -Highset O/C time expired 005 0001 No function assigned 006 0001 No function assigned 007 0001 No function assigned
The marshalling of the Target LED’s and alarm contacts are performed in a similarmanner to meet the end- customers requirements.
3.0 Conclusion
By following this simple example, more complex applications can be implemented on the7UT51 relays.The implementation of settings on the 7UT51 relays, and all Siemens relays in general,is best performed by creating a relay setting file in the DIGSI software, and using therelay manual for interpretation of settings. The settings can be printed to a text file using
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DIGSI, which can then be inserted into a setting document. The DIGSI file can be givento the customer to load directly to the relay.Although the 7UT51 relay provides the customer with numerous settings, only a fewsettings must be calculated and changed from the default settings for almost allapplication requirements. The default settings of the relay can protect all type of three-phase and single-phase transformers. Normally only setting the transformer and CT datais required. The differential settings remain unchanged, except to switch ON the 87function.
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