Dear all,
What is the relationship between protective relay and FACTS devices during power systems stress? Do the FACTS devices operate first or the protective relay is triggered first during the system stress? What is the operation sequence of these protection devices during emergency?
How are these two types of devices coupled with each other?
Kind regards,
Chao
What do you mean by 'system stress? Is it an overload, or fault condition?
The precise answer depends on the definition of system stress.
Here, the system stress means the abnormal fluctuations of voltage, current, frequency or phase in power systems, which is caused by the disruptive disturbances or fault conditions. The system stress could result in the overload of transmission lines. Thanks.
Kind regards,
Chao
Hello Chao again. The mentioned issue is related to the correct and normal operation of various components for restoring the normal state of the power system where the capability limits of components should not be violated under all circumstances for avoiding permanent damage of components or at least severe degradation of conditions.
In that sense, the FACTS devices should interact with abnormalities in a fast way relative to the protection actions. The time left for the FACTS to do proper corrective actions should be less than the time limit of component exposure to abnormalities for avoiding damage. Just before that time limit, the protective devices must handle the situation.
I am kindly inviting you to read tge relevant chapters in each volume of the dynamic security book. The main security issues are presented in chapter 1 of the first volume while there are several chapters about FACTS devices in volume 2. Your feedback will be appreciated.
https://www.researchgate.net/profile/Mohamed_EL-Shimy/publications?pubType=book
Dear Chao,
You are welcome. Your feedback will be highly appreciated. I also welcome any possible collaboration.
Best regards,
M. EL-Shimy
FACTS devices are reasonably fast and may at times prevent protective relay operation. For severe disturbances like faults the protection devices should operate. The FACTS devices are often helpful in restoration of the system after clearing of fault. There is a need to coordinate the response of FACTS devices to assess realistic system stresses, but the relay coordination based on equipment stresses need not be compromised. FACTS helps in dynamic response , voltage and reactive power control following a reasonable disturbance and during recovery period after a large disturbance. Hence the two issues have little conflict. FACTS studies may hint to extend the relay response time , but the protection engineers should use their own judgement from equipment safety point of view.
Hence I see no direct linkage except cross checking the improved margins with FACTS devices present.
system under stress does not corresponds to an extremely abnormal behaviour in power systems,so FACTS devices comes into operation quickly unless there is an alarming disturbance which requires the faster operation of relay or the protective devices.
A PSCAD type analysis of FACTS network shall bring out magnitudes of high Transient current and voltage stresses. As agreed by all of us extreme cases desirably must trigger the relay protection, but operational o/v and O/C can be taken care of by the o/v protection devices and o/c or cooling provided. Usually the silicon device protection limits are respected during design and system related stresses with FACTS devices should be lower unless some resonance or harmonic related stresses develop in filters. There are plenty of work on identification of faults in various types of FACTS DEVICES in lines and improving fault detection time . As I said earlier some self healing features in built in VSC based devices can be studied to see if protective relay operation can be avoided in some cases to improve availability of lines and equipments etc.
I agree with Ashok
There is lot of work to be done in this part of protection coordination in HV networks with FACTS. Several papers are written about this topic in IEEE transactions
Relays operates during abnormal conditions only whereas FACTS operates during normal conditions may also be used during abnormal conditions depending upon how we use it.
Relay switching time is also considered for controlling the relay operation time. That is, if the function of the instrument does not improve the system, then the relay operates.
To all those respondents who believe that FACTS devices necessarily improve system recovery from fault conditions, may I point that, yes, their controller response can be very fast but their overcurrent capability is usually very limited. Unless they have been grossly over-rated, they will not permit large flows of post-fault current, which may in fact degrade system recovery. Also, it seems to me that FACTS devices (with some exceptions) are typically designed to provide a balanced phasor response to the measured system conditions: so they will provide a controlled response in terms of P and Q flows. It remains to be seen how they will respond to unbalanced system faults or single -pole closures.
I agree with some of the answers .FACT may play its role for system post fault stability .Otherwise they have independent responsibilities for security,stability and dependability of the system for which they have been designed.Adaptive relaying is the solution for the system with FACTs.Pl.refer papers to explore the protection issues for the system with FACTs for better understanding .
James Toal has raised the right issue. FACTS devices can be and are very expensive if the device and component level current capabilities have to be high to cater to short circuit conditions , particularly the series devices.
It should be prudent to design FACTS for steady state and post recovery phases and avoid high current stresses through judicious firing or withdrawl of it. In any case controllers can't really help during the fault period. In practical FACTS projects often one finds a few more protection relay operations before stabilization . I know that the FACTS designers do spend days on RTDS to coordinate protection related matters . The academic world as found in many publications ignore some of the hard limitations of FACTS devices and the economics.