Surge Protection 1

[plc297]

Do lightning arresters go hand in hand with surge arresters in protection of motors? What motor sizes are usually protected? Any brands of arresters have been good in the past? I have had problems with compressors specially during lightning storms.

 

[dpc]

Lightning arresters and surge arresters are really the same thing. IEEE has stopped using the term "lightning arrester", I believe.

For good protection, you need surge protection on the primary side of the system (this is generally placed at the transformer primary), at the main secondary service panel, and possible at each motor.

Because of the wavefront nature of surge voltages, the closer the arrester to the device it is supposed to protect, the better the protection. Even a few feet can make a big difference. If possible, put surge arrester in the motor terminal box.

And good grounding practices are important as well. Keep grounding connections to surge arresters as short as possible with as few bends as possible.

Check the GE website for some good technical information on surge protection.

 

[rbulsara]

To add to dpc's post:

What size motors are we talking about here? Are they outdoors or indoors? I would think lightning arrestor or surge arrestor will be applied to large and typically MV motors.

At less than 600V level, more appropriate devices to employ would be transient voltage surge suppressors (TVSS) which is little different than a LA or SA. It dissipates/diverts much less energy and it is a supplement to a lightning arrestors, but not a substitute for them.

LA/SA could still pass (not operate) enough surge currents/voltage which can be deterimental to LV equipment and that is where TVSS are handy, besides protecting from transients caused by equipment internal to the building.

 

[jbartos]

Suggestion: IEEE Std 100 Dictionary considers surge arresters and lightning arresters synonymously
The surge arrester is actually defined, and lightning arrester is a synonym

 

[jbartos]

Suggestion: Visit

http://www.thomasregister.com

and type Arresters under Product or Service, which will return various types of arrestors (electric, spark, surge, lightning, etc.) and companies dealing with them

 

[electricpete]

I think that if any surge protectio at all is used at the motor, it is commonly surge capacitors, not arrestors. Arrestors are commonly used at other parts of the system.

The whole issue of surge protection is a tricky issue. Some users elect not to use surge caps even on 13.2kv motors. At our plant we have them on all 13.2kv motors but no 4kv or below motors.

Part does depend on the surge environment, including upstream protection. Vacuum breakers may tend to create some surges. Long runs of cable tend to lower the effect incoming surge from any source (other than direct hit). I have heard some people say that 100 yards of cable or more means no surge caps required.

One thing that goes very much hand in hand with surge protection is a discussion of the motor turn insulation capabilities: When you order a new or rewoudn motor, I think NEMA MG1 gives you some choices... 2.5pu or 3.5pu using terminology descirbed in ieee522. Requesting testing at 3.5pu will help ensure you get a better motor more resistant to surge. Some customers also get involved in analysing/specifying requirements for the insulation system beyond the surge test... i.e. dedicated turn insulation including number of layers of tape depending on voltage level.

 

[electricpete]

I should mention that the user who uses no surge caps on 13.2kv motors specified dedicated turn insulation and 3.5pu surge testing on initial purchase and rewinds. It is a very large electric power utility among the top few in the US.

Are the compressors outdoors? We have a lot of failures of outdoor motors during the most severe wind-blown rainstorms. Often tough to sort out lightning or moisture intrusion for us.

 

[jbartos]

Suggestion: Reference:
Robert W. Smeator "Switchgear and Control Handbook," Second Edition, McGraw-Hill Book Company, 1987, Pages 3-65 to 3-68:
Figure 44 Lighting Protective Equipment for a motor connected to an exposed overhead line
The protection consists of a surge capacitor that reduces steepness of a surge wave and lightning arrester (surge arrester) that protects the motor against lightning overvoltages.
Also, a reactor or inductance might be used to protect the motor in addition to the surge capacitor and lightning arrester.

 

[electricpete]

jb - I stand corrected. There may be situations where an arrester is provided directly at the motor (in addition to cap).

A more commmon situation that I have seen is that there are lightning arresters at the transformer.. and no overhead lines between transformer and motor. In this case, only lightning arresters at transformer, none at motor. Motor may have surge caps.

 

[jbartos]

Correction (I beg your pardon): The correct name of the Author is: Robert W. Smeaton

 

[gsimson]

Lightning protection is normally provided for the Power System as a whole and not just only for the motors.
Surge arresters are provided for the motors to prevent damages due to Switching surges - Switching on & Switching off.
I have come across an article 15 years back that motors of rating around 200 kW at 6.6 kV system and with the cable length of more than 200 m ( AND condition) are likeky to be affected by switching surges considering the inductance and capacitance of the system.
Surge voltages are generated due to current Chopping ( VCB, Air blast CB & one type of SF6 CB). These surges are suppressed by RC network.
Also surges are generated by restriking (due to L & C). These surges are suppressed by Metal oxide type arresters.
For better [erformance, the surge arresters are to be placed in the Motor terminal box, but generally not possible due to space constraints.
If found economical, both the types of arresters can be provided for motors upto 500 kW.
Transformers are also affected by switching surges generally when switched off. I will post the details if I can get hold of the article I was referring to.

 

[brucecranene]

How are capacitors sized for surge protection? Are capacitors rated for surge protedtion?

 

[busbar]

Limited surge-capacitor information at:

http://www.geindustrial.com/cwc/products?pnlid=4&famid=7&catid=33&id=capacrot&typeId=0

http://www.geindustrial.com/products/manuals/GEH-2730B.pdf

http://www.geindustrial.com/products/specs/capacrot_spec.pdf

 

[jbartos]

Comment on gsimson (Electrical) Dec 5, 2003 marked ///\\
I have come across an article 15 years back that motors of rating around 200 kW at 6.6 kV system and with the cable length of more than 200 m ( AND condition) are likely to be affected by switching surges considering the inductance and capacitance of the system.
///Please, notice that 200kW motor is very small for 6.6kV power supply. IEEE Standard 141-1993 (Red Book) indicates in Table 3-11 on page 92 that the motor should be 400kW minimum. Apparently, the surge problems were given a consideration.\\