What types of transient voltage protection is applied on medium voltage motors and are these types of protection that are applied depended on the type of motor it is e.g Synchronous vs Induction motor?
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2 Answers
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Medium voltage motors are protected with zinc oxide surge arrestors, surge protection capacitors and RC filters. The surge arrestors seem to be the most often used. When capacitors are used, they are used in parallel with surge arrestors. The use of RC filters is has been recommended by studies, but they may need to be custom designed for each installation.
For induction motors, purchasing motors with higher surge voltage withstand capability may be an option. Induction motor installations may include power factor compensation capacitors, but those capacitors may not have the proper characteristics for surge protection.
The mounting location and lead length to surge protection devices must be considered as part of the surge protection design.
Here is an example of MV surge arrestor construction:
Here is a complete 3-phase Controllix assembly with arrestors on top and a 3-phase capacitor on the bottom.
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\$\begingroup\$ Thanks for the hints that some statements were out-of-bounds. They have been removed. +1 \$\endgroup\$– user105652Mar 17, 2019 at 18:31
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\$\begingroup\$ You have listed three protection methods which are ZnO arrestors, surge protections capacitors and RC filters. Can all these methods be applied to both induction and synchronous motors? Doesn't the type of motor dictate which protection method can be applied? \$\endgroup\$– zarbtcMar 17, 2019 at 18:53
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\$\begingroup\$ These methods can be applied to induction and synchronous motors, transformers, and motor controllers. Manufacturers may have recommendations about specific product selection, but the methods and components are basically the same for all. \$\endgroup\$– user80875Mar 17, 2019 at 19:29
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Motors of most any type can benefit from RC snubbers across each phase winding. A 100nF capacitor across its power terminals with a common mode choke that power feed passes through will absorb and/or block most commutation noise. and possible increase the life of the motor.
You also have the option of using large 30mm or 40mm MOV's across the windings, or if a single source of power (universal) put the MOV there, along with a 100nF capacitor and a common mode choke. Universal motors create much HF noise on their power feeds, so these filters benefit more than just the motor.
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\$\begingroup\$ I am pretty sure the asker is referring to the power distribution and industrial motor definition of medium voltage about 1000 to 25000 volts. There are only induction and synchronous 3-phase motors in that world. \$\endgroup\$– user80875Mar 17, 2019 at 18:12
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\$\begingroup\$ I am referring to medium voltage motors rated 1000 to 44000 volts in my country. \$\endgroup\$– zarbtcMar 17, 2019 at 18:55
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\$\begingroup\$ There are ready-made surge suppressors for those voltage ranges, in steel cabinets, and they are not cheap. They have to put many 1,200 VAC MOVs in series and parallel to meet the labeled voltage/surge rating. The oil industry uses huge 5,000 HP motors to pump oil, and installs multi-tap surge protection at each motor. \$\endgroup\$– user105652Mar 17, 2019 at 19:06