surge damage

[ban-all-sheds]

Of course that is completely irrelevant to the OP's question.

Much of this thread is.

when electrical equipment is damaged from a transient peak power surge, does the damage occur when the power cuts off or when it reinstates, or can it be from either.

Why are you asking?

Have you suffered an incident of some sort?

 

[bernardgreen]

I understood your concern. That failure would result in low or no voltage.

On one phase yes, on the other two ( in the UK a star connected three phase 415 volt supply is distributed around and area or street. Each house taking one phase and neutral to get 230 v nominal supply.

 

[westom]

Each house taking one phase and neutral to get 230 v nominal supply.

And again, this is why bettter installations also have the all so important earth ground at each building. But again, that and the resulting voltages are completely irrelevant to what the OP asked.

 

[hapihari]

Of course that is completely irrelevant to the OP's question.

Much of this thread is.

when electrical equipment is damaged from a transient peak power surge, does the damage occur when the power cuts off or when it reinstates, or can it be from either.

Why are you asking?

Have you suffered an incident of some sort?

Yes. Good question.
I am awaiting manufacturers report, but trying to second guess why inverters which have been controlling typically 1.1kw pumps are failing on power interuptions after only 3yrs service. One theory is it could be capacitor break down resulting in bridge rectifier damage.
We are in the process of having type 2 surge protection fitted locally to supplement the type 1 fitted at the main switchboard. I will be interested to know if this will have the desired effect, and if so, should it not have been in the M&E build design spec.

 

[JohnW2]

I am awaiting manufacturers report, but trying to second guess why inverters which have been controlling typically 1.1kw pumps are failing on power interuptions after only 3yrs service. One theory is it could be capacitor break down resulting in bridge rectifier damage.

As I'm sure you know, failure on power-up (sometimes power-down) and, particularly rapid power-down/up sequences, is a very common (quite possibly the most common) failure mode of very many electrical and electronic (and, indeed, mechanical) things - and doesn't usually have anything to do with any sort of supply 'surges'.

Kind Regards, John

 

[bernardgreen]

What make are the inverters and do they have a wire wound resistor in series with the incoming mains ?

I was asked to look at why invertors on a number of production lines were failing too often when power was applied. They never failed during prolonged running. The failure was a limiting resistor intended to protect the diodes that rectified the mains to DC by limiting current while the capacitors were charging on power up. It was rated with a maximum voltage of 250 volts but during power up the resistor was taking the full mains peak of 325 volts until the capacitors were charged. This over volt caused breakdown of the insulation between adjacent turns in the resistor which resulted in a burn out of the wire at that point. Replacing it with a 400 volt rated resistor in over 50 units stopped the failures.

Edit I have sent you a PM with more details of the specific case.

 

[ricicle]

Have the invertors been wired correctly ?
Most of them that I have ever worked on do not like any form of line interuption (ie contactor) between the invertor and motor.

 

[bernardgreen]

Have the invertors been wired correctly ?.

Wired in compliance with the manufacturer's instructions. The manufacturer did not dispute the matter was a design fault (*) and did later change the type of resistor to one that would withstand the voltage across it during the in-rush current period. Another user of the same invertors had "solved" the problem by using zero crossing point switches to bring the invertors back on line.

(*) it might have been a cost conscious buyer who selected an "equivalent" resistor ( ohms and wattage ) without realising the maximum voltage rating was a critical one. Before anyone quotes Ohms law the resistor could be over driven in terms of wattage for short periods of time.

 

[ricicle]

Sorry Bernard, my question was for the OP.

 

[westom]

One theory is it could be capacitor break down resulting in bridge rectifier damage.
We are in the process of having type 2 surge protection fitted locally to supplement the type 1 fitted at the main switchboard.

Critical is not protectors. But how those protectors connect to earth. Not earth that is only a 'safety ground' (ie a receptacle). Earth that is an electrode in the ground. Critical to making that protector effective is even wire length, as short as possible (ie 'less than 3 meters'), to that single point earth ground.

Only earth ground must be single point earth ground. Making a connection that is too long or to different ground electrodes can actually increase damage to electronics. A protector without earthing will do little.

Another discussed a resistor on the incomng power line. Better designs do not use a resistor. A technology, even standard in 1950s designs, is an inrush current limiter. No design shold require one. The device is only used to make electronics more robust.

 

[hapihari]

What make are the inverters and do they have a wire wound resistor in series with the incoming mains ?

I was asked to look at why invertors on a number of production lines were failing too often when power was applied. They never failed during prolonged running. The failure was a limiting resistor intended to protect the diodes that rectified the mains to DC by limiting current while the capacitors were charging on power up. It was rated with a maximum voltage of 250 volts but during power up the resistor was taking the full mains peak of 325 volts until the capacitors were charged. This over volt caused breakdown of the insulation between adjacent turns in the resistor which resulted in a burn out of the wire at that point. Replacing it with a 400 volt rated resistor in over 50 units stopped the failures.

Edit I have sent you a PM with more details of the specific case.

Thanks for that. I wont purjure myself by naming brands, but if you like conumdrums, think of an anagram for 'TIT'!

 

[hapihari]

Have the invertors been wired correctly ?
Most of them that I have ever worked on do not like any form of line interuption (ie contactor) between the invertor and motor.

Fairly sure they were wired correctly.

 

[bernardgreen]

A technology, even standard in 1950s designs, is an inrush current limiter. No design shold require one. The device is only used to make electronics more robust.

How would you make an inrush current limiter ?

How can a design that requires capacitors to charge up on switch on not have an inrush currrent greater ( often much greater ) that the continuous steady state operating current..

 

[westom]

How would you make an inrush current limiter ?

Inrush current limiter is an electrical part that was used even in 1950 televisions. Many confuse it with an MOV. Examples:
http://www.alliedelec.com/search/se...:0&dsDimensionSearch=D:inrush+current+limiter

These devices are less often used since today's designs use more robust capacitors, diodes, and other circuits.

When a resistor is used as described, the resistor must often be a flame retardant type. For reasons irrelevant to the OP's problem.

 

[bernardgreen]

Inrush current limiter is an electrical part that was used even in 1950 televisions. Many confuse it with an MOV.

The example appears to become very hot in use. Not suitable for the application being discussed.

I pulled the file on the above case. The resistor was in circuit only as a limiter until the power supply was stabilised. At that point a relay operated to short out the resistor.

This design was just about acceptable when the invertor was continuously powered. It was the frequent removal of power during emergency stops that dropped the relay and bought the resistor back into circuit. Operators were opening covers to remove blockages and this was invoking an emergency stop condition which required all power to be removed to ensure no motors could move.