Transformer Overheating Even Under No Load

[npalen]

OP here. It's a simple three zone system with a toggle switch for each zone and roughly 200 ft of wire to each zone including the common. I had checked the resistance through each circuit coming up with about 50 ohms on two circuits and about 30 ohms on the third which had the bad solenoid since replaced.
The solenoids are rated at about 0.4 amps inrush and about 0.25 amps holding current. (24VAC)
At this point I'm thinking it must be the nature of these transformers to run very hot since replacing a new one with another new one. I need to ask the supplier to talk to the manufacturer to see if that is the case.

Edit: Redneck in training suggested above that there could be a DC component in the primary causing the heat. Is there any way this can be verified with a VOM? I'm not aware of any DC devices in the vicinity.

 

[Redneck in training]

OP here. It's a simple three zone system with a toggle switch for each zone and roughly 200 ft of wire to each zone including the common. I had checked the resistance through each circuit coming up with about 50 ohms on two circuits and about 30 ohms on the third which had the bad solenoid since replaced.
The solenoids are rated at about 0.4 amps inrush and about 0.25 amps holding current. (24VAC)
At this point I'm thinking it must be the nature of these transformers to run very hot since replacing a new one with another new one. I need to ask the supplier to talk to the manufacturer to see if that is the case.

Edit: Redneck in training suggested above that there could be a DC component in the primary causing the heat. Is there any way this can be verified with a VOM? I'm not aware of any DC devices in the vicinity.

If the sine wave is asymmetrical then the difference in area under the positive and negative curve is in essence DC. There is a device called power analyzer the can show it. Only problem is that they usually cost many thousand dollars. Typical maximum temperature rise of the transformer is about 50F over ambient. Needless to say that some small transformers will run significantly hotter.

Here is a link to DC in transformer winding. Look in section 18. Transformers Part 2 - Beginners' Guide to Electronics

 

[SPYDERLK]

If the sine wave is asymmetrical then the difference in area under the positive and negative curve is in essence DC. There is a device called power analyzer the can show it. Only problem is that they usually cost many thousand dollars. Typical maximum temperature rise of the transformer is about 50F over ambient. Needless to say that some small transformers will run significantly hotter.

Here is a link to DC in transformer winding. Look in section 18. Transformers Part 2 - Beginners' Guide to Electronics

I would look for a non zero reading on the DC scale of my meter while measuring the AC. If the wave is symmetrical it should hold close to zero.
larry