Shunt reactors are typically designed for natural cooling, with #radiators mounted directly on the #tank, it may be required to implement control measures in the cooling circuit depending on the state of the #shuntreactor's circuit breaker. Control actions can be initiated through the #circuitbreaker's auxiliary contact or by activating an #overcurrent relay adjusted to 50% of the reactor's rated current.
Upon energizing the reactor, the overcurrent #relay guarantees a secure control action, irrespective of the circuit breaker's #auxiliary #contact condition.
Electrical utilities have recently been advocating for the adoption of automatic shunt reactor switching to improve power system performance. This requires close monitoring of the busbar voltage level. The integration of this feature into a #multifunctional #numerical relay is considered a straightforward process.
It is crucial for the user to conduct a comprehensive evaluation of the relay's performance, considering the following factors:
An over/under voltage relay with a reset ratio of 1% or better is necessary for this application.
Generally, multiple over/under voltage levels with independently adjustable time delays are needed within the relay.
The over/under voltage relay should operate only when all three voltages are above or below the set operating level, or the relay must be able to measure and operate based on the value of the positive sequence voltage.
Traditional Protection and Control Schemes for Shunt Reactors
Multifunctional numerical #protection relays are commonly used to protect #power #transformers and shunt reactors. However, outdated protection schemes for shunt reactor protection, which include only a limited set of protection functions, are still frequently encountered.
Below are two examples of conventional protection configurations as illustrated in the subsequent figures.
Figure 1 – Typical Shunt Reactor Protection Scheme Number 1
A potential protection strategy includes employing restricted ground fault protection (87N) for reactor unit safeguarding. This system will instantaneously trip in the event of any internal phase-to-ground faults. Additionally, overcurrent protection (50/51) is utilized to detect internal phase-to-phase faults.
Ground overcurrent protection devices, like 50G/51G, act as a secondary line of defense against ground faults and serve as the primary protection against disagreements between circuit breaker poles.
Figure 2 – Typical Shunt Reactor Protection Scheme Number 2
The second protection scheme employs differential protection (87) for the reactor unit. This protection will instantly trip in the event of any internal phase-to-phase or phase-to-ground faults. Overcurrent protection, particularly 50/51, acts as a backup protection mechanism for internal phase-to-phase faults.
Residual #overcurrent protection, like 50N/51N, acts as a secondary defence against ground faults and the main protection against discrepancies in circuit breaker poles. It is noteworthy that numerical multifunctional relays possess significantly more functionalities than those depicted in the figures above.
For details on the proposed protection scheme for shunt reactors, including a multifunctional numerical protection relay, please refer to the subsequent chapter.
Conclusions
The paper offers a thorough analysis of HV shunt reactors, including their protection and control schemes. Figure 3 illustrates a potential #application for a multifunctional numerical relay employing a DFT filtering technique.
This will assist the end user in correctly selecting and applying the relay for #highvoltage shunt reactor protection and control.
Figure 3 – An example of a comprehensive HV shunt reactor protection and control scheme involves a multifunctional numerical relay.
All the protection and control functions depicted in Figure 3 are typical of multifunctional numerical transformer protection relays. Evaluating the appropriateness of a particular relay for a shunt reactor application is crucial.
Table 1 summarizes each function depicted in Figure 3, accompanied by some typical setting values. It should be noted that these suggested settings are intended as broad guidelines.
The purpose of this paper is to provide guidance for those in need of assistance with HV shunt reactor protection and control issues.
Table 1: - List of functions for complete HV shunt reactor protection and control scheme
Function | Comment | Typical setting shown in percent of the shunt reactor rating |
87=low impedance differential protection | Check suitability for shunt reactor application with relay manufacturer. | Set restraint differential level to 10-15% with 2nd harmonic restrain set at 10%. Set unrestraint differential level 200%. |
87N=low impedance, restricted ground fault protection | Check suitability for shunt reactor application with relay manufacturer. | Set differential level to 10%. Set operate angle for directional criteria to ±65 deg. Relay shall include adaptive 2nd harmonic restrain feature. |
#1-50/51=HV overcurrent protection | Backup protection, sensitive for internal faults close to the reactor bushings. | Set low set to 130% with time delay in between 0.6s and 1s. Set high set to 250% with time delay of 0.1s. * |
#2-50/51=HV overcurrent protection | Backup protection, sensitive for internal fault close to the reactor star point. | Set low set to 130% with time delay in between 0.6s and 1s. Set high set to 200% with time delay of 0.1s. * |
#3-50/51=HV overcurrent protection | Used as circuit breaker failure protection and indication that reactor is energized for the cooling control logic. | Set low set to 30% with appropriate time delay as CBF protection. Set high set to 50% in order to indicate that shunt reactor is energized. * |
49=thermal overload protection | Shall be used with great care. Shunt reactor overload can only be caused by overvoltage in a power system. That is the exact time when reactors are required to be energized. Thus it might come in conflict with shunt reactor voltage/reactive power control functionality in the power system. | Specific manufacturing data are required in order to properly set this function. Possible to use winding/oil contact thermometer instead. |
50G/51G=ground fault protection in reactor neutral point | Backup protection, sensitive for internal fault close to the reactor star point. Used for turn-to-turn fault detection logic. | Specific system data are required in order to properly set this function. |
50N/51N=ground fault overcurrent protection in reactor HV side | Backup protection, sensitive for internal faults close to the reactor bushings. | Set low set to 20% with time delay in between 0.6s and 1s or even longer. Use 2nd harmonic blocking. Set high set to 175% with time delay of 0.1s. * |
59N=unbalance overvoltage | Used for turn-to-turn fault detection logic. | Specific system data are required in order to properly set this function. |
67=directional ground fault protection | Used for turn-to-turn fault detection logic. | Specific system data are required in order to properly set this function. |
27&59=under/over voltage | Used for automatic shunt reactor control. Often more than one stage required. | Specific system data are required in order to properly set these functions. |
Document: | HV Shunt Reactor Secrets for Protection Engineers by Zoran Gajić, Birger Hillström, and Fahrudin Mekić, ABB | |
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Size: | 0.58 MB | |
Pages: | 30 | |
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