Terminals in the back but lateral side of the motor
Terminals in the back but lateral side of the motor
(OP)
Sir,
We have three old 180kw induction motors in our pump house. On the back but lateral side of the motors I saw terminals with ferrules s1 and s2. I could not understand the use of those terminals. I measured the resistance between the terminals and found that the value was in the order of kilohms. When the motor was energized I measured the voltage to neutral in both terminals as about 110 volts. The supply of the motor is three phase 415 volts.
What is the purpose of these terminals? I request for your valuable comments. Thanks in advance.
With regards,
Appunni
We have three old 180kw induction motors in our pump house. On the back but lateral side of the motors I saw terminals with ferrules s1 and s2. I could not understand the use of those terminals. I measured the resistance between the terminals and found that the value was in the order of kilohms. When the motor was energized I measured the voltage to neutral in both terminals as about 110 volts. The supply of the motor is three phase 415 volts.
What is the purpose of these terminals? I request for your valuable comments. Thanks in advance.
With regards,
Appunni





RE: Terminals in the back but lateral side of the motor
RE: Terminals in the back but lateral side of the motor
If not RTD it can also be strip heater terminals. Usually there are more than one RTD ina motor, one per winding at least. If there are only two terminals, then it is more likely to be a heater.
Measure the voltage between the s1 ans S2 when motor is running. RTD resistnaces could be easily relarted to a standard chart of RTD. Most common is PT-100 type RTD. You may need to do some trial and error.
RTD temp will change measurably with temp rise. A strip heater's R will not change significantly with temp.
RE: Terminals in the back but lateral side of the motor
RE: Terminals in the back but lateral side of the motor
RE: Terminals in the back but lateral side of the motor
RE: Terminals in the back but lateral side of the motor
DC injection braking (dynamic braking) is applied to stator terminals. Moreover, appunni has mentioned high resistance (kilo-ohms) between these terminlas so that rules anything connected with stator winding.
RE: Terminals in the back but lateral side of the motor
RE: Terminals in the back but lateral side of the motor
And yes, I am also keen to learn from "other experienced stator/armature rewinders"
RE: Terminals in the back but lateral side of the motor
RE: Terminals in the back but lateral side of the motor
As a "hands-on guy" with 20 years experience in rewinding all types motors, I can tell you that I have never come across such a braking winding. So, naturally I am curiuos to learn if such windings do exist.
Given the high resistance (kilo-ohms), I am thinking about the size of the conductor (really, really thin) and what current it can carry (really, really small)and how it will help in dynamic braking in this case (none, at all). So, if you can post some more details, I would be glad to change my view.
Btw, dynamic braking (using stator windings) has been in use at least since 1930's (yes, as a "theorist", I do have some really, really old books that describe the dynamic braking) and so, it is not so "modern" after all.
To cap it, I would say s1&s2 being thermistor leads is the most plausible explanation (as stated by scottyuk).
RE: Terminals in the back but lateral side of the motor
RE: Terminals in the back but lateral side of the motor
RE: Terminals in the back but lateral side of the motor
I agree that 110V across a thermistor would be interesting, although possibly shortening the life of the thermistor to milliseconds.
The original post noted that the 110V was measured relative to neutral, not across the thermistor. If the thermistor is embedded within the winding, there will be capacitive coupling between the sensor and its associated wiring, and the conductors of the winding. The coupling capacitance will be small, probably a few pF.
The instrument used to make the measurement will display a voltage dependant upon the voltage divider formed by the capacitance and the instrument input impedance. In the case of a modern DVM, the input impedance is very high, so it is quite possible to measure 'ghost' voltages which have no galvanic connection and are present solely due to parasitic capacitances between conductors close to each other.
On the other subject, I'm in agreement with Edison - I've never seen the winding arrangement you describe for DC braking, although that may merely prove my ignorance of motors from the dim and distant past. Are you sure this wasn't the starting winding for a 1-ph induction machine, which has similar characteristics (lots of turns, high resistance)?