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Can I Use VFD As a Power Supply for Mixed Load?

11/22/2012 4:58 AM

I am from India. I have one 3 phase, 415Vac, 11kW Variable Frequency Drive from Siemens. I have used it as a power supply for 3 phase, 415Vac, delta connected, 11kW induction motor. Can I use it as a power supply for 3 phase, 415Vac, 11kW heater? Can I use it as a power supply for lighting loads, particularly incandescent lamps?

The drive has 50/60Hz DIP switch. Currently, 50Hz position is selected. After selecting 60Hz DIP switch position and nominal motor ratings as rated voltage=115Vac, rated frequency= 60Hz, can I use it as a 3 phase, 115Vac, 60Hz power supply for supplying a mixed load of two 3 phase motors and one 3 phase heater (total 5kW) in US? If power supply of one motor is switched off through MCB, will the drive trip at restoration of the power supply?

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#1

Re: Can I use VFD as a power supply for mixed load?

11/22/2012 5:14 AM

As there is no need to introduce a variable speed drive to anything other than a motor, the concept of applying it to a heater or lighting is nonsensical and a total folly. Heater and lighting circuits are best protected by other equipment, leaving the drive as a device for varying the speed of a motor, as per its design intent.

One cannot reach the speed of light by using a variable speed drive!

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#2
In reply to #1

Re: Can I use VFD as a power supply for mixed load?

11/22/2012 5:53 AM

yeah u can use but it is unnecessary.........

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Guru
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#3
In reply to #2

Re: Can I use VFD as a power supply for mixed load?

11/22/2012 7:15 AM

Invitation declined. The concept is nonsense.

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#4

Re: Can I Use VFD As a Power Supply for Mixed Load?

11/22/2012 10:07 AM

It doesn't matter where you are from.

The answer is still NO! Why would you?

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Guru
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#5

Re: Can I Use VFD As a Power Supply for Mixed Load?

11/22/2012 1:30 PM

You cannot mix loads on the output of the VFD no matter what. the only loads that you can operate are 3 phase, the VFD is not made to deal with imbalanced current among the phases and will likely protect itself from that by shutting down. So if you have a 3 phase lighting or heating load that is balanced among the 3 phases, yes you can technically use it, that is often how we test drives. But as the others have mentioned, why? If you want a variable voltage supply for incandescent lighting and resistive heating, there are much less expensive ways of doing that which do not involve changing the frequency.

By the way, the 50/60Hz switch on the Siemens drives only does one function, it tells the display how to dea;l with the output values it shows you. Other than that, it serves no purpose. A VFD could not care less what the incoming power is, and the output is completely variable at all times.

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#6

Re: Can I Use VFD As a Power Supply for Mixed Load?

11/22/2012 1:42 PM

Dear Atul,

as already pointed out, it would be more logical to replace your motors and the heater [resistor] to allow direct operation at 415 V, 50 Hz (I'm assuming you want to use a US heater in India).

But if for some reason you want to use the heater without changing it, the 11 kW-rated VFD will probably drive a mixed 5 kW load (two fan motors + resistor) if you find the right parameter mix. But don't even try it on an 11 kW heater or with lighting loads. And yes, it may trip at restoration if switched off through MCB. Try longer ramps.

You will not be using the drive as a variable speed one. Protection may be limited. Your drive seems to be built for simple operation as a fixed frequency converter, since you even have that 50/60 Hz switch. I would expect it to be more tolerant to mixed loads, too.

brgds

Snel

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#7

Re: Can I Use VFD As a Power Supply for Mixed Load?

11/22/2012 5:59 PM

yers you can use it as a heater.....for about 2 seconds

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Power-User

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#8

Re: Can I Use VFD As a Power Supply for Mixed Load?

11/22/2012 10:31 PM

You should directly connect to heater without VFD.

Not clear why you want to use for VFD for the sake of it.

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#9

Re: Can I Use VFD As a Power Supply for Mixed Load?

11/23/2012 2:25 AM

Atul, why do you want to use a variable frequency source for a heating load or for incandescent lighting loads? A VFD (variable frequency device) is used for regulating frequency, and therefore the speed, of induction motors. Connecting VFD in a heater circuit, or a incandescent lighting circuit, will not achieve anything but add to the impedence of the circuit. Needless power loss will result.

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Guru

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#10

Re: Can I Use VFD As a Power Supply for Mixed Load?

11/24/2012 11:57 PM

One question only:

Why on Earth do you want to employ something really complicated to feed something primitive?!?

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Guru
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#11

Re: Can I Use VFD As a Power Supply for Mixed Load?

11/25/2012 9:35 AM

It seems Atul want the answer for viva question asked by some KHASOOT professor. I remember some questions of my college days:

1. In simple pendulum, in place of ball if an elephant is tied, what will happen?

2. If we make a through hole in earth passing through its center and drop this table in it, where it will go & why?

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Guru
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#12

Re: Can I Use VFD As a Power Supply for Mixed Load?

11/25/2012 1:35 PM

The only reason I can think of as to why you would want to do something like this is because your too cheap to have a proper power distribution or control system or you have not been properly trained in electrical control design.

Don't, especially since I doubt your lighting is three phase AND I think you will find this is illegal in the Indian and US electrical standards.

Do it the right and legal way!

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Fredski (1); iftikhar129 (1); jack of all trades (1); JRaef (1); leveles (1); lyn (1); pritam (1); PWSlack (2); Satish Saxena (1); shivaganti (1); Snel (1)

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