Surge Arrestors Locations in HV Substation

[rockman7892]

Besides the transformer primary and secondary terminals are there other locations in HV substations where it is best practice to install surge arrestor protection?

Is it best practice to typically include surge arrestor protection at incoming of HV substations (138kV/230kV) to protect equipment from surges and transients on incoming line when the incoming switch or breaker is open? Is it typical to provide on line side of HV breaker to protect breaker itself from surges? Is there any sort of decision criteria when determining arrestor in incoming vs just sticking with that on the HV terminal of transformer?

 

[RRaghunath]

Surge arresters are placed at the transformer terminals that connect to overhead power lines.
Further, the surge arresters are also installed at the incoming/outgoing overhead lines to/from the substation.
If there are cables/busducts, it is also important to install surge arresters at the transition points / on either side of bus duct / cable to safe guard the insulation.

 

[cranky108]

It is unusual to get lighting in a substation because of overheat shielding, so very few surge arresters are needed. The lines coming in should have arresters. And the arresters on transformers are sometimes more about the manufacturer warranty. That said, it is possible to get switching surges, and an arrester will be needed for those types of equipment.

 

[rockman7892]

Thanks for responses

In a particular situation i'm looking at the upstream utility feeder has arrestors on outgoing lines however customer owned substation downstream does not have incoming arrestors on incoming line. Customer owned substation is a standard design so line distance between utility substation and customer substation could vary depending on location.

My understanding has been to place arrestors on high side of HV breakers on incoming lines to protect breakers from surges or lightning strikes on overhead lines entering substation, when the breaker is open?

 

[rockman7892]

In looking at a design reference I came across the following statement:

At open circuit points, these waves are reflected back at nearly double the original rate of
rise, increasing the possibility of a flashover or equipment damage close to that point. It is apparent that
protection should be considered for the line entrances on large substations, especially where line breakers
and disconnect switches may be open, constituting dead-end reflections. Surge arresters will provide the
most effective means of protection, but line entrance gaps may be sufficient. Line entrance protective
gaps may be considered as an economical alternative to surge arresters at substation entrances of all
overhead lines 23 kV and above to provide additional protection for substation insulation under the
following conditions:

This supports the recommendation for arrestor placement at line entrances on the high side of breaker. I'm not familiar with "protective gaps"? Can anyone help explain this concept?

Another reference I found supports the statement above and indicates that breaker high side arrestors are recommended when breaker will be opened for long period of time without an isolation switch to isolate it from incoming surges.

 

[jghrist]

Protective gaps are just electrodes extending from each end of an insulator to make the flashover voltage lower than the BIL of equipment. A cheap way to ensure that equipment insulation does not break down. Problem is, it requires a momentary outage to break power follow current. A surge arrester self heals after discharging, eliminating the outage.

Arresters on the line entrances will protect the breakers unless they are a long distance from the line entrance.

 

[cranky108]

I don't think you can make other people do the right thing. You can make them do the safe thing, however, with standards and so forth. But arresters are not for the safety of people, they are for the safety of equipment.
Sometimes it is better for people to learn the hard way.

 

[bacon4life]

In my region we get very little lightning, so most transmission lines do not have overhead shielding and many substations do not have shielding. In some cases we have surge arrestors on incoming lines in addition to arrestors on the transformer banks. We have had several 115 kV surge arrestors fail during blue sky conditions while in service, so I am concerned that deploying additional arrestors might actually reduce overall reliability.

An engineer from a neighboring utility mentioned that they had begun putting 230 kV arrestors on many lines as they replaced oil circuit breakers with SF6 circuit breakers. The reasoning was something about the series resistors in a oil breaker being a much gentler way to avoid trapped charges versus a larger transient of an SF6 breaker.