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NSERC Industrial Research Chair in

Detecting fault generated surges in DC line of VSC HVDC Schemes for travelling wave based fault location

Fig. 2- Surge detection method

Fault locations were calculated using the timing obtained by comparing the Rogowski coil output signals with a threshold.

The system was calibrated by calculating the propagation velocity by applying a test fault at a known location (1 km from rectifier side).

This Research investigated the detection of travelling waves in a VSC

based HVDC cable for fault location purposes. Results show that travelling waves can be detected through the

surge capacitor currents, if a series inductor is present between the cable and the converter terminal.

If no series inductor is in the system, a small series inductor can be inserted for fault location purposes

Using the surge capacitor and Rogowski coil combination, DC line faults in VSC HVDC schemes can be located accurately

HVDC transmission systems that carry large amounts of power and important for system stability.

Quick repairing of permanent faults HVDC transmission lines/cables is essential for minimizing the down time and outage costs

Fast and accurate fault location is required to initiate repair work.

Fault location in HVDC transmission systems is usually carried out using travelling wave based fault locators.

Most of the existing HVDC line fault locators (LFLs) are designed for traditional line commutated convertor (LCCs) based HVDC schemes.

The objective of this research is to examine the applicability of currently used LFL technology for VSC based HVDC schemes.

A fault generates travelling waves that travel at a constant velocity denoted of v. Propagation of the travelling waves can be illustrated on a lattice diagram:

Using the initial travelling wave arrival times at two terminals (tR1 and tI1) the distance to the fault can be estimated using (1).

Most LFLs used in conventional LCC HVDC schemes use surge capacitor current to detect and measure the arrival of fault generated travelling waves .

This works well because the large DC smoothing reactors in LCC HVDC schemes essentially decouple the line side and converter side voltages at high frequencies.

The VSC topology does not require a DC smoothing reactor for its functionality

VSC appears as an ideal voltage source due to large DC bus capacitor.

Thus a clear surge will not be visible in the terminal voltage.

In practice, an inductor is installed between the line/cable terminal and the converter to reduce the rate of change of current through IGBT’s during DC line faults.

The presence of a series inductor should allow detection of travelling waves using the same arrangement even for the case of VSC HVDC.

Ip

l

L RC

ZE(t)

I(t)

Vr

Vr

dx

αHA

Ip

Ns :number of turns A :cross-section area (𝑚2) l :length (m).

Fig. 3 – Rogowski coil and Rogowski coil equivalent circuit

H : magnetic field intensity dx : length of a small element along

the loop α :the angle between the directions

of H and dx E(t) :induced EMF on the Rogowski

coil

𝜑 = total flux linked with the coil, M = mutual inductance between the primary conductor and the Rogowski coil. Using the equivalent circuit output voltage of the Rogowski coil can be calculated as,

Ampere’s and Faraday’s laws give induced EMF on the Rogowski coil,

Surge capacitor currents for a solid L-G fault at 200 km from the rectifier side. The fault occurs at 5.01s.

Fig. 4- Test System (Surge capacitors: 100 nF , Series inductors: 10 mH)

Fig.5- Surge capacitor currents (a) Rectifier side (b) Inverter side, with and without series Inductors

5.008 5.01 5.0120

50

100

150

Volta

ge k

V

(a) Time S5.008 5.01 5.0120

50

100

150

Volta

ge k

V

(b) Time S

5.008 5.01 5.012-10

0

10

Curre

nt A

(c) Time S5.008 5.01 5.012

-5000

0

5000

Curre

nt A

(d) Time S

5.008 5.01 5.012

-0.2

0

0.2

Volta

ge V

(e) Time S5.008 5.01 5.012

-0.2

0

0.2

Volta

ge V

(f) Time S

Fig.6 - (a)- Rectifier side line current (b)- Inverter side line current (c)-Rectifier side line voltage (d)- Inverter side line voltage (e)- Rectifier side Rogowski coil voltage (f)- Inverter side Rogowski coil voltage (red lines show the thresholds)

Sensitivity of the surge capacitor current to series inductor and surge capacitor

K.P.A. N. PATHIRANA1, A. D. RAJAPAKSE1, O. M. K. K. NANAYAKKARA1, R. WACHAL2 University of Manitoba1 (CAN), Manitoba HVDC Research centre2 (CAN)

www.cigre-canada.org Congrès 2012 CIGRÉ Canada www.cigre.ca

CIGRÉ-052

Travelling wave based fault location

Introduction Surge arrival time measurement system

Modeling of Rogowski coil

Simulation studies

Results

Conclusions

Typical variations of the terminal voltages, currents and the Rogowski coil voltages for solid L-G fault 290 km away from the rectifier are shown in Fig. 6

Fig. 1- Travelling wave based fault location

Converter side Cable Side

Surge Capacitor

Rogowski Coil

Inductor

𝐼𝐼𝑐𝑐 ∝d𝑉𝑉d𝑡𝑡

𝑉𝑉𝑟𝑟 ∝ d𝐼𝐼𝑐𝑐d𝑡𝑡

Sync. Generator

AC System

Cable (300 km)

Xf

vv

Rogowski coil

T1 T2

𝑉𝑉𝑟𝑟

𝐼𝐼𝑐𝑐

E(𝑡𝑡) = −𝑑𝑑𝜑𝑑𝑑𝑡𝑡

= −𝜇𝜇0.𝐴𝐴.𝑁𝑁𝑠𝑠𝑙𝑙

.𝑑𝑑𝐼𝐼𝑝𝑝(𝑡𝑡)𝑑𝑑𝑡𝑡

= −𝑀𝑀 𝑑𝑑𝐼𝐼𝑝𝑝(𝑡𝑡)𝑑𝑑𝑡𝑡

(2)

𝑉𝑉𝑟𝑟(𝑡𝑡) = −𝑀𝑀 𝑑𝑑𝐼𝐼𝑝𝑝(𝑡𝑡)𝑑𝑑𝑡𝑡

− 𝐿𝐿.𝑑𝑑𝐼𝐼(𝑡𝑡)𝑑𝑑𝑡𝑡

− 𝐼𝐼(𝑡𝑡).𝑅𝑅 (3)

Table 2 Actual and Calculated fault locations

Fault Location Error (m) Fault Location Error (m) Actual Calculated Actual Calculated

1 1.000 0 200 200.301 301 2 1.564 436 250 250.038 38

10 9.278 722 290 290.722 722 50 49.962 38 298 298.436 436

100 99.770 230 299 299.000 0

Table 1 Peak surge capacitor currents

series inductance Surge

capacitance 100 mH 10 mH 2 mH

200 nF 45.4 A 40.3 A 29.1 A 100 nF 22.7 A 20.2 A 14.5 A 20 nF 4.6 A 4 A 2.9 A

Sync. Generator

AC SystemT1 T2

tR1

tRI1

tI1

tI2

vvCable

Xf

𝐹𝐹𝐹𝐹𝐹𝐹𝑙𝑙𝑡𝑡 𝐿𝐿𝐿𝐿𝑐𝑐𝐹𝐹𝑡𝑡𝐿𝐿𝐿𝐿𝐿𝐿 (𝑋𝑋𝑓𝑓) =12

[𝐿𝐿 − (𝑡𝑡𝑅𝑅1 − 𝑡𝑡𝐼𝐼1). 𝑣𝑣 ] (1)

Distance

Tim

e

5.009 5.01 5.011 5.012 5.013 5.014-25

-20

-15

-10

-5

0

5

Ic (A

)(a) Time S

5.009 5.01 5.011 5.012 5.013 5.014

-80

-60

-40

-20

0

20

Ic (A

)

(b) Time S

with Ind.without Ind.

with Ind.without Ind.