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Re: Best way to handle poor electric delivery
To: CRTech <crtech@crtech.org>
Subject: Re: Best way to handle poor electric delivery
From: Terry Cowan <tcowan@knlr.com>
Date: Wed, 5 Apr 2017 09:36:58 -0700
In-reply-to: <CAB42DVqnnChU0cG+C8SqyfUNy1nZpJSP1E5e3=TLtmtyW+c6JQ@mail.gmail.com>
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Tom is partially correct.

Both an open delta and a closed delta will have 3 "hot" legs and a ground.  One leg will be significantly higher than the other two called "the high leg or teaser".  An open delta has two transformers and a closed delta 3 transformers.  The open delta should be avoid at all costs for transmitters as there is a lack of balance between the legs.  It also has less power available than a closed delta. 

The other option is a Wye or Star connection which uses three transformers and all legs are the same voltage to neutral.  The advantage is that all legs may be used for 120 v circuits.  This disadvantage is that the line to line voltage is 208 rather than 240.  Transmitters usually have a "tap" on the power transformer to accommodate 208 - 240.
Here is a link to a good article on the subject.
http://www.engineeringradio.us/blog/2012/02/the-open-delta-three-phase-service/

Terry Cowan
KNLR/KNLX

On 04/05/17 08:39, Tom Van Gorkom wrote:
Do you have true 3 phase power with one 3 phase transformer and three lines plus ground feeding it or is it open delta with 2 lines plus ground and usually two smaller transformers?

Until we insisted that the power company give us true 3 phase power, our AM site suffered constant TX power supply failures, A/C compressor failures, tower light fuses blowing, etc from the surges. Open delta can be determined also by a "wild" leg - one of the three lines coming into the building will be a higher voltage (~210 VAC) in respect to ground than the other two (120 VAC). They should all still be about 220-240 leg to leg. It's a lousy system that power companies like to use to save money but they are unbalanced with no path for line surges or the transmitter harmonics except to circulate in it's power transformer and other devices and blow them out. I understand that in some locations, you can insist that they change to true 3 phase because their installation is damaging your equipment.

We had to push hard and provide and install all the underground wiring and building installation. The power company paid for running new lines from the road to the edge of our property pole, the transformer and connections.

As a last resort, you can install the older type motor-generator 3 phase generator or a new solid state type. either one will have periodic maintenance.

Tom Van Gorkom
Radio Esperanza Engineering, KRIO AM/FM, KOIR FM
Office: 956-380-8150  
Cell: 865-803-7427

Rio Grande Bible Institute
4300 S US Hwy 281
Edinburg, TX 78539

On Wed, Apr 5, 2017 at 10:24 AM, Solomon Bachman <sbachman@kcbi.org> wrote:

Hey All,

 

I’d like to get some suggestions on cleaning up 3 Phase power in the middle of nowhere coming from a co-op. I have surge suppression on the mains and under the breaker with the transmitter but I am still cooking the input side of the 2500w modular power supplies every time there is storm.

 

The large surge suppressor on the incoming electric is older, so I am looking at replacing that since it is probably past its prime in surge dissipation. Are there any other tips/tricks/devices I should look at?

 

Solomon N Bachman | Chief Engineer

 

KCBI 90.9 FM  |  Dallas-Fort Worth

Encouraging Music…Words of Hope

750 N Saint Paul St.

Suite 1050

Dallas, TX 75201

www.kcbi.org

 

O | 469.801.7022

C | 817.523.9523

F | 214.468.9164

 



Follow-Ups: RE: Best way to handle poor electric delivery
(Solomon Bachman <sbachman@kcbi.org>, 5 Apr 2017 19:09:27 -0000)
References: Best way to handle poor electric delivery
(Solomon Bachman <sbachman@kcbi.org>, 5 Apr 2017 15:24:55 -0000)
Re: Best way to handle poor electric delivery
(Tom Van Gorkom <tomvangorkom@gmail.com>, 5 Apr 2017 15:39:43 -0000)
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