Delta Electronics VFD-EL C.1 Capacity Formulas, n T + n s k s − 1 = P C 1 ⎢ ⎢, n T + I M ⎢1+

Appendix C How to Select the Right AC Motor Drive

C.1 Capacity Formulas

1. When one AC motor drive operates one motor

The starting capacity should be less than 1.5x rated capacity of AC motor drive

The starting capacity=

k ⋅ N	⎛	GD	2
	⎜
	⎜TL +	375
973 ⋅η ⋅ cos ϕ ⎝

N ⎞

⋅⎟ ≤ 1.5 ⋅ the _ capacity _ of _ AC _ motor _ drive(kVA) tA ⎟⎠

2.When one AC motor drive operates more than one motor

2.1The starting capacity should be less than the rated capacity of AC motor drive

„Acceleration time ≦60 seconds

The starting capacity=

k ⋅ N	⎡		ns	⎤
	[nT + ns(ks − 1)] = PC1⎢⎢1	+		(ks − 1)⎥⎥	≤ 1.5 ⋅ the _ capacity _ of _ AC _ motor _ drive(kVA)
η ⋅ cosϕ			nT
	⎣			⎦
	⎢			⎥

„Acceleration time ≧60 seconds

The starting capacity=

k ⋅ N	⎡		ns	⎤
	[nT + ns(ks − 1)] = PC1⎢⎢1	+		(ks − 1)⎥⎥	≤ the _ capacity _ of _ AC _ motor _ drive(kVA)
η ⋅ cosϕ			nT
	⎣			⎦
	⎢			⎥

2.2The current should be less than the rated current of AC motor drive(A)

„Acceleration time ≦60 seconds

⎡	nS ⎛	⎞⎤	≤ 1.5 ⋅ the _ rated _ current _ of _ AC _ motor _ drive( A)
nT + IM ⎢1+	⎜ kS −1⎟⎥
⎣	nT ⎝	⎠⎦

„Acceleration time ≧60 seconds

⎡	nS ⎛	⎞⎤	≤ the _ rated _ current _ of _ AC _ motor _ drive( A)
nT + IM ⎢1+	⎜ kS −1⎟⎥
⎣	nT ⎝	⎠⎦

C-2 Revision August 2008, 2ELE, V1.02