A large set of fault cases was developed for the dynamic transient testing of line protection for a new 230 kV transmission line recently commissioned by Manitoba Hydro.
Transient simulation testing of protection offers many advantages over the more traditional (fundamental frequency) methods. Since the transient waveforms produced represent realistic voltage and current waveforms that the protection sees in service. The overall confidence in the testing results is greatly increased. And, the process to develop a transient system simulation model from a traditional phasor-based system is not difficult.
Accurate System Model:
It is possible to develop a study system that produces the same results as a fundamental frequency program. Once the positive and zero sequence networks are confirmed, the development of particular study cases of interest can be performed. The generated voltage and current test waveforms are then injected into the protection system using a transient playback system, allowing a thorough confirmation of the protection performance. The generated transient fault waveforms include all of the transient effects, such as DC offset, high frequency ringing, point on wave etc.
The Test Plan
Manitoba Hydro’s "D72V" is a new transmission line with a portion of it constructed on the same towers of an existing line, and on the same right of way (ROW) with some additional existing lines. During some preliminary state simulation testing of the relay, the directional ground overcurrent elements of the relay were giving some questionable results for some current reversal conditions due to mutual coupling effects. It was not clear whether the operation of these fast reacting elements was affected by the unrealistic instantaneous simulation of the transition between states, or by different fault conditions such as fault inception angle or prefault line loading. It was determined that a time domain analysis of the protection system was in order. The sensitivity of the forward and reverse ground overcurrent elements 67F and 67R of the Nxtphase L-PRO relay on the new D72V line was the focus of the transient test plan.
Figure 1: Manitoba Hydro System Model for generation of test waveforms
A number of time domain simulations were performed on the system model to generate the required testing waveforms. An "A" phase to ground fault was applied at one end of D36R, at Fault Location F3 on Figure 1, in order to produce a forward reverse current flow on he new line D72V. The application of fault angle was modified from 0 to 180 degrees in 30-degree steps; and the power flow from the Dorsey station to St. Vital on D72V was adjusted from 0, 100 and 200 MW. In addition, the telecommunications delay between line D36R breaker opening at the Ridgeway Station, B1 shown in Figure 1, and the breaker opening at the Dorsey end, B2 also shown in Figure 1, was selected at 30 or 100 msec. This set of tests was performed using a batch run feature of the PSCADTM power system simulation software, generating a total of 42 test cases. Each test case generated the three voltage and three current signals required for the transient time domain testing of the Dorsey and St Vital D72V protection system. An example of the waveforms applied is shown in Figure 2.
Specifically, using the system model, 200 MW is initially flowing on the new D72V line. A SLG fault is applied at Ridgeway end of the D36R line. The voltage and currents presented are recorded at the Dorsey end of D72V. When the fault is applied, the D72V relay at Dorsey end sees reverse current. The Ridgeway breaker opens 50 msec (3 cycles) after the fault, changing the direction of the current as seen at the Dorsey end of D72V. The breaker on D36R remote from the fault opens 30 msec after the local end (approximately 2 cycles) and removes the fault current flow from D72V.
These generated fault waveforms were then used for real time field testing of the new line using IEEE Comtrade format waveforms and a test set such as the Doble F6000 series.
Results of the Protection Testing
The forward and reverse ground overcurrent elements 67F and 67R of the Nxtphase L-PRO relay used on the new line were verified over a large number of test cases during a one-day field testing period. It was confirmed that the relay operation was not dependent on the prefault loading, fault inception angle or the protection telecommunication delay on the line, but that the level of positive sequence component of the fault current does have an impact on the operation of the directional ground overcurrent elements.
The use of fully transient test waveforms represented the realistic voltage and current waveforms that the protection will see in service. This increases Manitoba Hydro’s confidence that the test plan was realistic and fully exercised the line protection before the commissioning of the transmission line. n
REFERENCE
[1] "PSCAD/Relay Installation and Operations Manual", Manitoba HVDC Research Centre, Aug 2001.
M.S. Sachdev, T.S. Sidhu, P.G. McLaren, Issues and Opportunities for Testing Numerical Relays, IEEE Power Engineering Society Summer Meeting, Seattle, Washington, USA, 16 – 20 July 2000.
Transient simulation testing of protection offers many advantages over the more traditional (fundamental frequency) methods. Since the transient waveforms produced represent realistic voltage and current waveforms that the protection sees in service. The overall confidence in the testing results is greatly increased. And, the process to develop a transient system simulation model from a traditional phasor-based system is not difficult.
Accurate System Model:
It is possible to develop a study system that produces the same results as a fundamental frequency program. Once the positive and zero sequence networks are confirmed, the development of particular study cases of interest can be performed. The generated voltage and current test waveforms are then injected into the protection system using a transient playback system, allowing a thorough confirmation of the protection performance. The generated transient fault waveforms include all of the transient effects, such as DC offset, high frequency ringing, point on wave etc.
The Test Plan
Manitoba Hydro’s "D72V" is a new transmission line with a portion of it constructed on the same towers of an existing line, and on the same right of way (ROW) with some additional existing lines. During some preliminary state simulation testing of the relay, the directional ground overcurrent elements of the relay were giving some questionable results for some current reversal conditions due to mutual coupling effects. It was not clear whether the operation of these fast reacting elements was affected by the unrealistic instantaneous simulation of the transition between states, or by different fault conditions such as fault inception angle or prefault line loading. It was determined that a time domain analysis of the protection system was in order. The sensitivity of the forward and reverse ground overcurrent elements 67F and 67R of the Nxtphase L-PRO relay on the new D72V line was the focus of the transient test plan.
Figure 1: Manitoba Hydro System Model for generation of test waveforms
A number of time domain simulations were performed on the system model to generate the required testing waveforms. An "A" phase to ground fault was applied at one end of D36R, at Fault Location F3 on Figure 1, in order to produce a forward reverse current flow on he new line D72V. The application of fault angle was modified from 0 to 180 degrees in 30-degree steps; and the power flow from the Dorsey station to St. Vital on D72V was adjusted from 0, 100 and 200 MW. In addition, the telecommunications delay between line D36R breaker opening at the Ridgeway Station, B1 shown in Figure 1, and the breaker opening at the Dorsey end, B2 also shown in Figure 1, was selected at 30 or 100 msec. This set of tests was performed using a batch run feature of the PSCADTM power system simulation software, generating a total of 42 test cases. Each test case generated the three voltage and three current signals required for the transient time domain testing of the Dorsey and St Vital D72V protection system. An example of the waveforms applied is shown in Figure 2.
Specifically, using the system model, 200 MW is initially flowing on the new D72V line. A SLG fault is applied at Ridgeway end of the D36R line. The voltage and currents presented are recorded at the Dorsey end of D72V. When the fault is applied, the D72V relay at Dorsey end sees reverse current. The Ridgeway breaker opens 50 msec (3 cycles) after the fault, changing the direction of the current as seen at the Dorsey end of D72V. The breaker on D36R remote from the fault opens 30 msec after the local end (approximately 2 cycles) and removes the fault current flow from D72V.
These generated fault waveforms were then used for real time field testing of the new line using IEEE Comtrade format waveforms and a test set such as the Doble F6000 series.
Results of the Protection Testing
The forward and reverse ground overcurrent elements 67F and 67R of the Nxtphase L-PRO relay used on the new line were verified over a large number of test cases during a one-day field testing period. It was confirmed that the relay operation was not dependent on the prefault loading, fault inception angle or the protection telecommunication delay on the line, but that the level of positive sequence component of the fault current does have an impact on the operation of the directional ground overcurrent elements.
The use of fully transient test waveforms represented the realistic voltage and current waveforms that the protection will see in service. This increases Manitoba Hydro’s confidence that the test plan was realistic and fully exercised the line protection before the commissioning of the transmission line. n
REFERENCE
[1] "PSCAD/Relay Installation and Operations Manual", Manitoba HVDC Research Centre, Aug 2001.
M.S. Sachdev, T.S. Sidhu, P.G. McLaren, Issues and Opportunities for Testing Numerical Relays, IEEE Power Engineering Society Summer Meeting, Seattle, Washington, USA, 16 – 20 July 2000.
