440V system to 400V system - induction motors, hazardous area 2

[DrDrreeeaaa]

Hi All

I have been asked to look at a job we are doing where the supply authority is upgrading the supply transformer and in doing so the system voltage is going to change from the previous 440V to the new 400V mandated by IEC standards.

The site is a hazardous area and the plant I am concerned about are some three phase induction motors which are used to pump petrochemicals.

The motors have 'Ex' ratings for use in a Zone 1 area under the IEC regulations. The motors are in the range 22-40 kW and have nameplate voltage of 415V delta. The motors are old and no manufacturer's data is available.

The reduction in system voltage from 440V to 400V, with a utilization voltage of 380V (5% max voltage drop) is going to do the following as far as I can see however I am interested in what everyone thinks:

-Increase motor current draw
-Increased draw will lead to further losses, more heat generated
-I am concerned that this increased current is outside the motor's certification however certification documents are not available
-The motor will draw higher current at rated load and hence should be derated (%30)?

This is a result of the supply authority changing the nominal system voltage to 400V. Previous voltage should have been 415 but was 440 due to oddball HV/LV transformer.

How has everyone else managed this situation, where you have an existing site where the supply is changed/upgraded and the utility has decreased the supply voltage. This is due to the change to bring the supply voltage in line with IEC recommendations.

Is it a case of ensuring the existing devices on site can operate at 380/220V? What if they cant? Surely the supply authority can't just change your voltage requiring you to replace half your devices? or submains?

 

[ScottyUK]

If you're a European site then check the ATEX certification. We're a legacy petrochem site with our LV system running at the upper end of the 415V tolerance range, and we have found that the ATEX certifcation for a standard 400V motor won't cover us at our operating voltage. We've had to buy 415V nominal motors, which are available but not ex-stock.

In Europe the 400V nominal voltage was at the bottom end of the 415V tolerance and the top end of the 380V tolerance: equipment with either nominal voltage "should" work satisfactorily.


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If we learn from our mistakes I'm getting a great education!

 

[juleselec]

By the sounds of it, if the motors are rated Zone 1 and are in the range 22-40kW, then they are likely to be Ex d or Ex e. The installation conditions on Ex d are usually pretty limited and mainly relate to flamepaths, but there are often more specific conditions for installing Ex e motors.

However you have one big problem here - there are no HA certificates for the motors, which may or may not be illegal in itself. But whatever the legality, it certainly makes it impossible for you to implement any plant modifications that include these motors (and changing the supply voltage is a plant modification).

If I were the engineer signing off on any plant modifications, there'd be no way I'd sign off without valid haz area certificates. So unfortunately, the certs either need to be found or the motors need to be replaced.

 

[DrDrreeeaaa]

Thanks mate

It's an Australian site located in Western Australia, so AusEX, IECEx are accepted, but ATEX requires conformity assessment.

Unfortunately the motors are approx 20 years old (Brook Crompton, Newman motors) and the certifications are lost.

The 'tolerance' you're talking about is that a standard quantity?

The motors are 415V nameplate rated, I assume they are intended for use on a 440V system? But you're saying that if the certification permits a utilization voltage range unde the 415V nameplate that goes as low as 380V then it may be suitable?

What's your engineering opinion on the effect that the increased load currents are going to have... The plant has been operating for 40 years on 440V, this change will increase load current by about 10%...The existing cabling is not in great condition.

I guess that without a certification for the motor I am not permitted to make changes to the installation in any case...

 

[DrDrreeeaaa]

Yes spot on jules thanks for your input

 

[juleselec]

Another option is to write down all the serial numbers on the motors and call up Brook Crompton - by all rights, they should have copies of the HA certificates for those specific motors in their database.

But chances are that the certificates were issued under the old AusEx scheme, have already expired and were never renewed. This is a major complication with plant modifications on old legacy equipment. You may be able to get away with a letter of no objection from a third-party assessment, but it's equally likely that you'll just have to replace them.

 

[DrDrreeeaaa]

I have tried to jump through these particular hoops on this plant before.

I have had no luck chasing certificates for these motors by contacting the manufacturers, most have been bought out by other companies a couple of times by now and none of them were able to help. The motors have BS standards on their nameplates.

'letter of no objection' are you talking about a conformity assessment? I have looked at this and it would cost almost the same as a new motor. In addition, the motors are in poor condition, no evidence of insulation testing etc. that would be required under the certification.

I may have to negotiate with the supply authority to provide the new service with the same system voltage as the old service (440V but this will also be tricky...

 

[juleselec]

Yep you're right, it's called a conformity assessment now.

 

[waross]

I ran into a similar problem. A 480 Volt plant was being moved into a new building and new location. The utility would only supply 600 Volts at the new location. A combination service entrance and MCC were used with a transformer section. Two auto transformers connected in open delta were used to drop the 600 Volts down to 480 Volts.
I your place I would consider a pair of special order auto-transformers and continue running on the legacy voltage.

Bill
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"Why not the best?"
Jimmy Carter