69V Line to Neutral Voltage

[js1960]

Hello Fellow members,

I have a limited knowledge of transformer wiring configurations as they are applied in the field. However, I have run into some some situations that require 3 Phase power with 120V L-L/69V L-N voltages.

I would like to know, are there any "typical" applications that require this voltage? If so, are they industry specific, device specific, discpline specific, or "some other" kind of specific?

Also, it would be helpful to know if there is a "typical" transformer configuration used to produce this voltage?

Finally, bringing the answers to the above questions together (sort of), is the resulting 3 phase voltage end up being balanced between phases in both magnitude and displacement angle?


Thanks in advance

 

[davidbeach]

69V is a fairly common VT secondary voltage, but I'm not aware of any other application. A wye with 120V line-line will have 69V line-neutral.

 

[Skogsgurra]

Hi,

A YYn (or DYn) transformer will give you that voltage. Never seen the 69 V (L-N) being used. That doesn't mean it can't be used.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[dpc]

It's used in relaying and metering applications - sometimes by choice, sometimes by necessity.

Power is never delivered to a customer at 69 V that I'm aware of (in the US), and I've never seen it used in a commercial or industrial application.

 

[tinfoil]

120V 3-wire 3 phase delta is an 'ancient' supply voltage that you still find from time to time (my utility offered it in the 30s and 40s).

Perhaps someone 'modernized' some services by converting them to 4 wire but wanted to use the same old motors, etc.

 

[mikey70]

You did not say if this was an instrument transformer or power transformer. As has been mentioned this is a common secondary voltage for instrument transformers. Distance relays that require phase to phase voltage normally use the 67 volt (phase to ground) vt winding giving them 120 volts phase to phase which is the nominal rating of many relay coils. Digital relays can "do the math" so they usually can be wired either 3 wire or 4 wire and let the realy calculate all the necessary quantities. Electromechanical ground relays sometimes require the 120 volt winding to be wired in broken delta for polarizing.

 

[js1960]

Mikey70

I am interfacing Power meters to the system, monitoring Watts, Vars, VA, PF, etc. Therefore, the PTs and CTs are primarily for instrumentation. Unfortunately, I don't often get to look at the wiring diagrams of the systems that the meters are going into, so I don't know what else is hanging off the transformers besides power meters. This is the jist of my question .... what else could be on the transformer that would necessitate 69V l-n. Your response (and others) has given me a good general idea & I appreciate it. Typically (but not always) we are using analog type meters with no output to a DCS, so they are used by an operator as an indication to "do something" if the power consumption rises to high or falls to low.

Digging a little further (and changing the topic to this thread) what exactly does the term "distance relay" mean and how is one used? Also, for a digital relay, does the user configure it for 3W or 4W in advance and then it "does the math" to sense a proper drop out point of the relay?


Thanks,

 

[davidbeach]

Distance is a bit of a misnomer since that isn't what is measured, but it is the affect generally achieved. A distance relay is really an impedance relay, measuring the impedance from the relay to the fault. Since impedance is proportional to distance, the relay is known as a distance relay. Generally used on transmission lines.

Numeric relays need to be told whether voltages are connected 3W or 4W and the VT ratio. From there they can calculate anything they need to know about the voltage on the system.

With the newer relays there seems to be a drift toward using a 208Y/120V secondary on the instrument transformers rather than a 120Y/69V secondary. Both are common and sometimes both can be found in the same gear. It becomes especially fun when you need to do sync check with one side being 120V and the other side being 69V.