IEEE Std C37.230-2020 pdf download

IEEE Std C37.230-2020 pdf download.IEEE Guide for Protective Relay Applications to Distribution Lines.
Advantages of uni-grounded systems include the following:
Overvolages on unfaulted phascs are small, usually below 1.4 p.u.
Intermittent are voltages are avoided.
Transtformer windings near the neutral do not see high voltages even during ground faults, which
permits a less expensive graded insulation of the entire winding.
Disadvantages of unigrounded systems include the ollowing:
Grounding study is needed to evaluate and address ground and step potentials.
4.1.1.4 Resonant-grounded system
Resonant-grounded systems are most ofien applied in Europe. In this method, the substation transformer neutral is grounded through a reactance, also known as a Petersen coil (iiguteo 7). The reactance is resonantly tuned to the fundamental frequency with the stray capacitance ol all feeders connected to the same transformer.
The value of reactance is approximately determined by Equariom (1). In the case of a ground fault (C phase- to-ground fault in Figure 8). if properly tuned, the neutral reactor and the system stray capacitance will cause the same amount of fault current to flow in opposite directions through the point of fault, canceling each other. Figuto & and Figure 9 ilustrate fault current contribution by the system stray capacitance (solid-line arrows) and by the neutral reactor (dashed-line arrows). Since it is impossible to entirely match values for the neutral reactor with the system stray capacitance, a small amount of ground fault current will flow through the faul, but the majority of current will return to the source through the reactor. Small mismatches between the reactance and system capacitance (below 25%) will not create protection problems.
Advantages of a resonant-grounded system include the fllowing:
Ground fault currents are small.
Ares are self-extinguished.
Touch and step voltages are small.
The need for maintenance of the switches is reduced.
For a phase-to-ground faul on the system, it is possible to operate for a period of several hours, even when the fault persists. increasing reliability.
The slf-extinguishing feet exerted by the compensation reduces the possility of a single-phase-to-ground fault developing into a mutiphase fault. Intermittent ground faults are avoided.
Disadvantages of a resonant-grounded system inelude the fllowing
In protection systems using Iraditional technology, the reliability and sensitivity of the relays is reduced.
The dificulty of locating faults is increased.
Arrester protective levels are higher.
Insulation may need to be increased due to neutral shifting during transients.
It is not fctive in case of arcing cable faults.
Cables can produce repetitive and harmful restrikes.
Tuning can be difficult to adjust for varying system configurations such as those associated with distribution systems. During a single-phase-to-ground faul, the phasc-to-ground voltages of cach unfaulted phase inerease by a factor approaching V3. Due to cconomic considerations, this limits implementation of this type of grounding to lower voltage systems since line-to-line voltage rated insulation would be required.
The increased voltage raises the probability of simultaneous ground faults developing due to inereases in weak points in the system.
The first two drawbacks are being overcome with the development of fault detection and protection technologies (see [B65]). Due to the last two draw backs, to make it possible to adopt the resonant grounding system, a preliminary analysis will have to be made of effeets that the voltage surges in sound phases might have on insulation in the electrical system. To prevent any harmful ffects, it will be necessary to ascetain the weak points in the system and to check that all equipment has been designed to support new voltage demands. See 7.13 for methods of detecting ground faults on resonant-grounded systems.