Overvoltage Protection

[Hfuda]

A three-phase four-wire system has 380V LL, 220V LN voltages. A number of single phase 220V loads are connected between each phase and neutral. If the neural gets accidentally disconnected from the source, the 230V LN jumps to 380V LL. I am installing an overvoltage protector that can protect up to 300V. However, I am not sure what is the maximum voltage that the input terminals can accept without damage to the protector device? The specs do not provide an answer other than the fact that overvoltage setting can range from 270V to 300V. This implies that it can tolerate voltages above that. But to what level? And for how long?

 

[berkeman]

Welcome to PF.

What power levels are we talking about here? What are the main breakers rated at for this 3-phase system? Can you post a link to the protection device datasheet?

 

[DaveE]

It's likely the energy or power dissipated in the OVP device that causes their failure. Hence @berkeman's question about upstream protective devices. Voltage is only part of the data you need. Think of this as a system, not a single device.

 

[Ivan Nikiforov]

I am well aware of this problem. I design such electrical installations. If you use the TN-C system (combined working and protective neutral, that is, PEN), the protection against neutral breakage is performed as follows: 1) reliable re-grounding of the neutral conductor (PEN conductor) is performed at the input to the electrical switch cabinet; 2) a voltage monitoring relay is used, which controls the release of the input circuit breaker. If you use the TN-S system (separated operating and protective neutral, that is, N and PE), neutral break protection is performed only by using a voltage monitoring relay that controls the release of the input circuit breaker. The N wire is not re-grounded, the PE wire is re-grounded. The control circuit with the voltage monitoring relay is designed so that the input circuit breaker is switched off if the relay is defective. This relay protection circuit ensures voltage control in case of any voltage deviations.

 

[Ivan Nikiforov]

The use of surge arresters or surge protection devices to protect against neutral conductor breakage is unknown to me personally. The fact is that such devices are used for large overvoltages, for example, a lightning strike in an electrical line. Such devices practically do not respond to an increase in voltage from 220V to 380V, since they have a nonlinear characteristic of the dependence of resistance on voltage.

 

[DaveE]

The use of surge arresters or surge protection devices to protect against neutral conductor breakage is unknown to me personally. The fact is that such devices are used for large overvoltages, for example, a lightning strike in an electrical line. Such devices practically do not respond to an increase in voltage from 220V to 380V, since they have a nonlinear characteristic of the dependence of resistance on voltage.

Yes, this. Devices that can clamp voltages that accurately tend to be small, like TVS diodes, which can't absorb much energy. You could monitor the voltages and trip upstream circuit breakers, but this is complex and expensive for an unusual failure mode. It may also not be fast enough to save the downstream equipment anyway. Electrical distribution, done right, is usually pretty reliable, mechanically. If a neutral is broken, someone probably did it sort of on purpose. You can't protect against everything.