2.8 Variable Frequency Drive Brake Component Selection Guide

2.8.1 Selection of Resistance Value

During braking, the regenerative energy of the motor is almost entirely consumed in the braking resistor.
According to the formula: U*U/R=Pb
● In the formula, U represents the braking voltage for stable braking of the system
(For different systems, the value varies. For a 380VAC system, it is generally taken as 700V)
● Pb represents the braking power

2.8.2 Power Selection of Braking Resistor

Theoretically, the power of the braking resistor should be consistent with the braking power, but considering a derating factor of 70%,
the formula becomes: 0.7Pr=PbD
● Pr represents the power of the resistor
● D represents the braking frequency (the proportion of the entire working process occupied by the regenerative process)

For different applications, the following braking frequencies can be considered:

• Elevators: 20%~30%
• Unwinding and coiling machines: 20%~30%
• Centrifuges: 50%~60%
• Occasionally braked loads: 5%
• General cases: 10%

2.8.3 Selection Table for Inverter Braking Components

Inverter Power	Recommended Braking Resistor Power	Recommended Resistance Value for Braking Resistor	Braking Unit	Remarks
1.5KWT4	150W	≥220Ω	Standard Built-in	No special instructions
2.2KWT4	250W	>200Ω	Standard Built-in	No special instructions
3.7KWT4	300W	≥130Ω	Standard Built-in	No special instructions
5.5KWT4	400W	≥90Ω	Standard Built-in	No special instructions
7.5KWT4	500W	≥65Ω	Standard Built-in	No special instructions
11KWT4	800W	≥43Ω	Standard Built-in	No special instructions
15KWT4	1000W	≥32Ω	Standard Built-in	No special instructions
18.5KWT4	1300W	≥25Ω	Built-in optional	Append “B” to the inverter model number
22KWT4	1500W	≥22Ω	Built-in optional	Append “B” to the inverter model number
30KWT4	2500W	≥16Ω	Internal Optional	Add “B” to the inverter model number
37KWT4	3.7 kW	≥16.0Ω	External	VFDBU-35-B
45KWT4	4.5 kW	≥16Ω	External	VFDBU-70-B
55KWT4	5.5 kW	≥8Ω	External	VFDBU-70-B
75KWT4	7.5 kW	≥8Ω	External	VFDBU-70-B×2
90KWT4	4.5 kW×2	≥8Ω×2	External	VFDBU-70-B×2
110KWT4	5.5 kW×2	≥8Ω×2	External	VFDBU-70-B×2
132KWT4	6.5 kW×2	≥8Ω×2	External	VFDBU-200-B
160KWT4	16 kW	≥2.5Ω	External	VFDBU-200-B
200KWT4	20 kW	≥2.5Ω	External	VFDBU-200-B
220KWT4	22 kW	≥2.5Ω	External	VFDBU-200-B×2
250KWT4	12.5 kW×2	≥2.5Ω×2	External	VFDBU-200-B×2
280KWT4	14 kW×2	≥2.5Ω×2	External	VFDBU-200-B×2
315KWT4	16 kW×2	≥2.5Ω×2	External	VFDBU-200-B×2
355KWT4	17 kW×2	≥2.5Ω×2	External	VFDBU-200-B×2
400KWT4	14 kW×3	≥2.5Ω×3	External	VFDBU-200-B×3
450KWT4	15 kW×3	≥2.5Ω×3	External	VFDBU-200-B×3

(Note: “×2” indicates two braking units used in parallel, each with its own braking resistor. “×3” has the same meaning as “×2”.)

This selection table provides guidance data. Users may choose different resistor values and powers based on actual conditions (but the resistance value must not be less than the recommended value in the table, while the power can be greater). The selection of braking resistors needs to be determined based on the power generated by the motor in the actual application system, which is related to the system’s inertia, deceleration time, and the energy of potential load. Customers need to choose based on actual conditions. The larger the system’s inertia, the shorter the required deceleration time, and the more frequent the braking, the greater the power and the smaller the resistance value needed for the braking resistor.

NEXT

Explore these documents to learn more.