Electrical machines got a plate which attaches to the body of such machines. This motor plate consists the most important Motor Information Systems of the certain electrical motor. This gives very useful information to the user which regard different upper limits for the safety operations of such machines. The details of such machines are different according to the types of electrical machines. Following are several important common details which were shown in the plate of electrical motors.
1. Rated Frequency of electrical motor:
Rated frequency is the fundamental frequency of the three-phase supply system on which the machine is include in operating without any modification.
2. Rated Power of the motor:
Rated power is the maximum continuous shaft power of the motor which can deliver without any exceeding safe internal temperature limits. Safe internal temperature limit is specify as also a rated temperature rise. This is not so often found in some item plate in electrical motor data plate.
3. Rated Voltage of electrical motor:
Rated voltage is the ram value of the line voltage of three phase supply at rated frequency. This current a safe no load current below its critical threshold value. An excessive price of no-load current will be seeing if we attempt to raise the line voltage above the rated voltage and rated frequency.
Normally a variable three-phase supply at rated frequency for this stuff. We run the motor on no-load by applying a reduced voltage & then raise the voltage slowly by keeping an eye on the ammeter which measures no-load current.
At one point the ammeter reading tends to raise fast and this is known as knee point of magnetic saturation. The rated voltage will be taken as the voltage which little below this threshold value, to comply with standard voltage value is possible.
4. Rated current of electrical motor:
Rated current is the RMS value of the line current when the motor is operate at the rated power at rated voltage and rated frequency. The motor can be adjusted for rated current through but it will take long testing hours unless we know the visibility of the rated power.
If it is general purpose cage rotor motor the full load slip will arrive 5% and this gives us a clue to design on the load for the test. That means the motor is load at a corresponding speed to 5% we need to run the motor for several hours at this load and then measures the temperature rise. Next, we can check the temperature rise is near the rated temperature rise of that motor.
5. Rated volt-ampere range
(VA) rated= 3 V rated.I rated
6. Rated Duty
Rated duty indicated whether the motor can be operate continuously or not. There are three basic types of duties such as.
- Continuous Rated Duties ( Continuous duty motor are specified with letter “Cont” )
- Short time duties (Show in specified time limits in minutes such as 5, 10, 15, 60 mins)
- Intermittent duties ( Specified with duty factors such as 10% 20% 30% ..)
This is an extreme per unit value of permissible output power under rated other operating conditions. Typical service factor for general purpose motor is about 1:10.