How to calculate a relay for a three phase motor load? example:
U：400V
P：15KW
Efficiency: 0.8 for a motor < 5KW
Efficiency: 0.9 for a motor > 5KW
Power factor: 0.8 for a motor < 5KW
Power factor: 0.9 for a motor > 5KW
V3 = 1.732
Nominal current absorbed by the motor:
The current rating of the relay must be 4 * I of the motor in order to withstand starting currents: >>> 106.8 A >>> it’s necessary to take a 125 A relay.
Advantages of Solid State Relays in comparison to a electromechanical relays ?
Because of their semiconductor technology-based design, SSRs provide a higher degree of reliability, longer life and reduced electromagnetic interference (EMI), as well as faster response times and vibration and shock resistance, when compared to the EMR counterparts. This is due to the fact that SSRs have no mechanical contacts to wear out or arc, which is the primary cause for EMR failure.
What does “zero-voltage turn-on” mean? (or synchronous or zero-cross)
The relay will only turn on when the mains (output) voltage is near zero.
What does instantaneous or random turn-on mean?
When the control voltage is on the relay will switch on at the same moment, whatever the mains voltage value.
In what application would I use a zero voltage turn-on V. a random turn-on relay?
Zero-cross relays are used with resistive loads while random turn-on relays are used with inductive loads (motors, transformers, coils etc.).
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