How do you calculate power saving in VFD?

EXAMPLE

1. Step 1: 60 hp × 0.746 = 44.76 kw1
2. Step 2: 0.28 ratio × 44.76 kw1 = 12.53 kw2
3. Step 3: 0.88 ratio × 44.76 kw1 = 39.39 kw3
4. Step 4: 39.39 kw3 – 12.53 kw2 = 26.86 kw4
5. Step 5: 26.86 kw4 × 8,760 hr × $0.12 per kwh = $28,235 (annual savings)

How do you protect a VFD from a short circuit?

When a variable frequency drive is not approved for overload protection, or if multiple motors are fed from the VFD, one or more external overload relays must be provided. The most common practice is to use a motor overcurrent relay that will protect all three phases & protect against single phasing.

How much current does a VFD use?

VFDs bring motors up to full speed quickly and by drawing only 100% to 150% of full load amps (FLAs). This ability to start at normal FLA is very important if the power supply cannot withstand the normally six times FLA across-the-line starting draw, or even the 350% FLA soft-start device current.

How many amps does a VFD draw?

Its nameplate full load amps are 25… with the drive in bypass it draws ~21. Through the VFD at 60 Hz it’s at 25, almost a 20% increase from directly connected.

When to increase the size of a circuit breaker for a VFD?

If you are sizing a circuit breaker for a VFD, you need to increase the size to accomodate the additional harmonic currents. The scale factor is dependent on the drive input circuit. Some drves have no inductors resulting in very peaky currents with higher supply losses.

What do you need to know about VFD sizing?

VFDs do not produce torque. VFDs supply current that, with the correct voltage and frequency, makes the motor run at the desired speed. VFD sizing should always be based on motor current and voltage, not hp. Let’s begin with the basics by learning how to read a motor nameplate.

Can a VFD be connected to a 50hp motor?

So if you have a VFD rated for 100HP but it is connected to a 50HP motor, you MUST size the conductors for the max amp rating of the VFD, not the motor. You can then use a smaller breaker if you so desire, but most people just size the breaker for the conductors.

What can be used as overcurrent protection for a VFD?

Either circuit breakers or fuses can be used as the overcurrent protection for a VFD. Fuses are less likely to have nuisance outages than circuit breakers, and are a better option for circuits that have a high-fault current.