Automatic frequency unloading ?ccording to policy ENTSO-E

[Fpias]

I have a problem with the use of automatic frequency offloading devices that must comply with the policy ENTSO-E. Previously, in Ukraine, the total operating time of automatic frequency unloading devices was 0.3 s, and according to the policy, the operating time should be in the range of 0.1-0.15 s. When the value was set to 0.1s. our frequency unloading devices began to operate falsely. Can any of you share your experience, which devices that have the function of controlling the frequency and response time (type and manufacturer) comply with the policy ENTSO-E and what parameters are set in your electrical networks according to frequency for such devices, for example, setting the response time, setting the blocking when decrease in measured voltage, rate of frequency decrease? Thank you for understanding and help.

 

[bacon4life]

I see that P5 – Policy 5: Emergency Operations requires 0.15 s, is that the policy you are referring to?

My region ULFS plan (USA-WECC) requires total clearing time of 0.233 s (14 cycles at 60 Hz). Based on extremely high NERC compliance fines for failing to clear within 14 cycles and the direction to have "no intentional time delay", I assume most UFLS loads actually disconnect quite a bit earlier.

The language in both plans about "No intentional time delay" can mislead engineers to set the relay with an operating time of zero. However, many relays use a simple frequency detection algorithms that can be confused by phase angles changing during faults. I have seen several relay with frequency measurement time of less than 3 cycles misoperate. Depending on the specific relay vendor, the frequency element pickup times can either include or exclude the a reasonable frequency detection period. Thus for identical clearing times, I would set one vendor to 81PUD= 0.00 s and the other vendor I would set 81PUD = 0.07 s.

The WECC plan specifically prohibits electromechanical frequency relays. I assume this prohibition was added in the 1990's after finding poor performance of legacy relays during a set of large blackouts.

 

[System Protection]

@bacon4life

Do you supervise your UFLS elements with an undervoltage element?

 

[bacon4life]

Yes.

 

[Fpias]

Absolutely right. This is P5 – Policy 5: Emergency Operations. The Central Dispatch Service of Ukraine requires the fulfillment of these conditions. The reaction time, taking into account the shutdown time of the high-voltage breaker, should be no more than 0.15 s from the moment the frequency begins to drop according to the specified parameter. The minimum operating time of our frequency relays is 0.15 s, if we add to this time the operating time of the intermediate relay (0.01 s), the reaction time of the automatic circuit breaker control device (0.04 s) and the shutdown time of the high-voltage circuit breaker (0.08 s. for a 10 kV breaker), then the total time will be 0.28 s. which does not comply with P5 – Policy 5: Emergency Operations requirements. To identify relay protection devices whose frequency response time would be up to 0.1 s, I tried to test the ABB REF 615 terminal based on the FRPFRQ function. The minimum response time by frequency is 0.08 s (4 periods for a frequency of 50 Hz), and taking into account the operating logic it is 0.1 s. I want to check a similar function for a Siemens terminal based on Siprotec 5. What frequency relays do you use that would correspond to the P5 – Policy 5: Emergency Operationsin their parameters?

 

[bacon4life]

Newer installations use SEL-451 relays, with legacy locations using an older Siemens relay.

What is your automatic circuit breaker control device? I am not familiar with something that would add 2 cycles of delay. Our relays are have output contacts wired directly to the circuit breaker trip coil.

 

[Fpias]

Thank you very much for your answer. For automatic circuit breaker control we use relay from ABB, type REC 670, and relay from Siemens Siprotec 4, type 7VK611. We use intermediate relays to multiply contacts for shutdown circuits, signaling circuits and in the circuit of the central emergency event recorder (for old substations). 2 delay cycles gives REC 670.

 

[bacon4life]

Do you currently use a separate frequency relay with a 0.15 s operating time, plus a 0.04 s delay in the REC 670? It looks like the underfrequency element in the REC 670 can be set for a 0.070 s operating time.

 

[Fpias]

Yes, we use a separate frequency relay. In the frequency function block REС 670, the minimum time setting is only 0.08 s. We want to use the frequency function block in the REC 670, but the datasheet does not have a function block diagram and does not fully describe the operation of the function block elements. Representatives of the plant also cannot clearly tell us how the unit works. Therefore, we do not know what correct parameters to set. We're trying to figure it out.

 

[stevenal]

[URL unfurl="true"]https://library.e.abb.com/public/77e14a51c87d49aeba777e288ec93530/NextECMUpload_1874426_20200221161922.pdf[/url]

 

[Fpias]

Thank you so much for the link!