2 speed motor control help.

[Cavie]

Not much knowledge with motor controls and motors. I have two cooling towers with 2 speed motors controled by dual contact starters. Tower one runs on high speed with both contactors pulled in. Tower two runs on high speed with only one contactor pulled in. Tower two startes out with both contactors pulled and drops the lowspeed contactor out after about 30/45 seconds. Which one is working correctly? The Metasys system is also confussed!

 

[jim dungar]

Not much knowledge with motor controls and motors. I have two cooling towers with 2 speed motors controled by dual contact starters. Tower one runs on high speed with both contactors pulled in. Tower two runs on high speed with only one contactor pulled in. Tower two startes out with both contactors pulled and drops the lowspeed contactor out after about 30/45 seconds. Which one is working correctly? The Metasys system is also confussed!

There are two different types of two-speed motors. They use different control schemes. It sounds like you have one of each kind.

A separate winding motor is basically two motors in one. Its control scheme is uses one contactor for high speed and a different contactor for low speed.

A consequent pole motor has windings that get reconnected for the different speeds. Its control scheme uses one contactor for one speed and both contactors for the other speed. In your case it is probably a variable torque motor so the normal scheme is: low speed is the first contactor and high speed is both.

 

[Cavie]

There are two different types of two-speed motors. They use different control schemes. It sounds like you have one of each kind.

A separate winding motor is basically two motors in one. Its control scheme is uses one contactor for high speed and a different contactor for low speed.

A consequent pole motor has windings that get reconnected for the different speeds. Its control scheme uses one contactor for one speed and both contactors for the other speed. In your case it is probably a variable torque motor so the normal scheme is: low speed is the first contactor and high speed is both.

Motors are the same. Identical towers. 3 phase 480 volt. Disconects at the motors only break one set of wires. Don't know if motors switch from high to low and back during normal operation. Light blubs on MCC burned out but that is another matter and I have no control over it. I've only noticed the motors running on high speed any time I'm near the towers.

 

[jim dungar]

Motors are the same. Identical towers. 3 phase 480 volt. Disconects at the motors only break one set of wires. Don't know if motors switch from high to low and back during normal operation. Light blubs on MCC burned out but that is another matter and I have no control over it. I've only noticed the motors running on high speed any time I'm near the towers.

I have never tried to have both contactors of a separate winding motor pulled in at the same time. I can't imagine it will cause any type of mis-operation but I really haven't given it any thought. It will probably waste energy by energizing windings that are doing no work.

A separate winding starter will have (2) 3-pole contactors, a consequent pole start will have (1) 3-pole and (1) 5-pole contactor.

Two speed motors require 6 leads to the starters, so if you only have 3-pole disconnects maybe someone bought 2-speed starters to control 1-speed motors. What do the motor nameplate show?

 

[Cavie]

Two three pole contactors a the mcc starter. Six wires to the motor. Disconect breaks three set. I'll climb the tower on Monday and check the nameplate.

 

[jim dungar]

Two three pole contactors a the mcc starter. Six wires to the motor. Disconect breaks three set. I'll climb the tower on Monday and check the nameplate.

Then you have a separate winding controller.

If your disconnect is only a 3-pole unit, what happens to the other conductors?

 

[Cavie]

Then you have a separate winding controller.

If your disconnect is only a 3-pole unit, what happens to the other conductors?

DONO. They pass thru the disconect and up yo the motor.

 

[benaround]

DONO. They pass thru the disconect and up yo the motor.

Cavie, First thing you need to get is (2) 6 pole disconnects, you can't just

break 3 out of 6 conductors to the motors. Second thing you have to wire

the motors up correctly, following the diagram on the motors. It also may

help you to 'goggle' 2 speed motors, or something like that. The last time I

wired cooling towers they were 2 speed, 6 conductors from each mcc bucket,

and the motors were 12 lead. I also installed 6 pole disconnects. Without

knowing what kind of motors, or how many leads, this is the best I can do.

 

[Cavie]

Cavie, First thing you need to get is (2) 6 pole disconnects, you can't just

break 3 out of 6 conductors to the motors. Second thing you have to wire

the motors up correctly, following the diagram on the motors. It also may

help you to 'goggle' 2 speed motors, or something like that. The last time I

wired cooling towers they were 2 speed, 6 conductors from each mcc bucket,

and the motors were 12 lead. I also installed 6 pole disconnects. Without

knowing what kind of motors, or how many leads, this is the best I can do.

There is evidence of somebody rewireing. Old piping and abandoned disc. I'll look into it further on Monday.

 

[Cavie]

Correct 6 pole disc found downstream. Part problem solved. At MCC starter, two 3 pole contactors. High speed contact: T4,T5,T6 show 266 volts 9 amps . Low speed contact: T1,T2,T3 show 8.5 volts and 5 amps. low speed contact is not on. Based on this, I have determined that one of the Metasys sensing coils is bad. The coils have adjusting screws that I do not know how they work or what they control. I'm trying to determine which of the starters is working correctly. Both fans are running properly (at least both are on high speed). One showing two coils with red lights indicating current flow. One showing 1 bright red light and one dim red light. Am correct in assuming the the 8.5 volt 5 amp is a back feed from the motor sensing voltage controlling the system and telling it when to drop back into low speed for economy? Wires runing off t1,2,3, to other parts of the starter.

 

[jim dungar]

Correct 6 pole disc found downstream. High speed contact: T4,T5,T6 show 266 volts 9 amps . Low speed contact: T1,T2,T3 show 8.5 volts and 5 amps.

What the the reference for your voltage readings?
For proper troubleshooting you would need to know:

T1-T2
T2-T3
T3-T1
T4-T5
T5-T6
T6-T4
L1-L2
L2-L3
L3-L1
L1-G
L2-G
L3-G
T1-G
T2-G
T3-G
T4-G
T5-G
T6-G

If these are separate winding motors, you should not be getting any feed back from one speed to the other except for some minor phantom voltages (transformer action - because of the common steel in the motor stator).

 

[Cavie]

Just did basic line to ground check for voltage. Have no Idea where the 8.5 volts is coming from or why the 5 amp reading on the low speed contact. There are 3 other fuses in the bottom of the starter. Two psysically smaller then the third. Didn't have time to check everything. There were more important issues to deal with this morning.

 

[Strahan]

From what I read you have a 2speed 2winding three phase starter Both motors are identical. One seems to be working properly meaning one contactor is energized at a time. I'm not sure of what the outcome would be for both to be energized at once but if this is the case obviously nothing serious. I would check for a possible faulty interlock between the two starters.

 

[benaround]

Cavie,

Sounds like you have 6 lead motor.

L1 L2 L3

6 4 5 1,2,3, join together HIGH SPEED 2 wye

1 2 3 4,5,6, stay open LOW SPEED 1 delta

 

[jim dungar]

Cavie,

Sounds like you have 6 lead motor.

L1 L2 L3

6 4 5 1,2,3, join together HIGH SPEED 2 wye

1 2 3 4,5,6, stay open LOW SPEED 1 delta

You are describing a 2-speed consequent pole motor, which requires a 5 pole contactor for one speed and a 3-pole contactor for the other speed.

The OP has (2) 3-pole contactors, which is the proper control device for a 2-speed separate winding motor (which also has 6 leads).