Delta Electronics VFD-G manual Capacity Formulas, When one AC motor drive operates one motor

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 _ rated _ capacity _ of _ AC _ motor _ drive(kVA) t A ⎠

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

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

„Acceleration time ≦60 seconds The starting capacity=

k ⋅ N [nT + ns(ks − 1)] = PC1⎢⎢1 + ns			(ks
	⎡
η ⋅ cosϕ	⎣	nT
	⎢

„Acceleration time ≧60 seconds The starting capacity=

k ⋅ N [nT + ns(ks − 1)] = PC1⎢⎢1 + ns			(ks
	⎡
η ⋅ cosϕ	⎣	nT
	⎢

⎤

− 1)⎥⎥ ≤ 1.5 ⋅ the _ rated _ capacity_ of _ AC _ motor _ drive(kVA)

⎥

⎦

⎤

− 1)⎥⎥ ≤ the _ rated _ capacity _ of _ AC _ motor _ drive(kVA)

⎥

⎦

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

„ Acceleration time ≦60 seconds

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

„Acceleration time ≧60 seconds

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

2.3 When it is running continuously

„The requirement of load capacity should be less than the capacity of AC motor drive(kVA) The requirement of load capacity=

k ⋅ P

η ⋅ cosϕ ≤ the _ rated _ capacity _ of _ AC _ motor _ drive(kVA)

„The motor capacity should be less than the capacity of AC motor drive k ⋅ 3 ⋅VM ⋅ IM ⋅10−3 ≤ the_ rated _ capacity_ of _ AC _ motor_ drive(kVA)

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

k ⋅ IM ≤ the _ rated _ current _ of _ AC _ motor _ drive( A)

C-2 Revision July 2008, EG03, SW V1.06