[Antennas] Ground rod questions (Ground currents)

[Milt, N5IA]

----- Original Message ----- 
From: "Eric Lemmon" <wb6fly at verizon.net>
To: <Antennas at mailman.qth.net>
Sent: Wednesday, July 01, 2009 4:21 PM
Subject: Re: [Antennas] Ground rod questions (Ground currents)


Chris,

Perhaps your statement is true in some states, but not in the central part
of California where I live.
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That is a Delta system you are describing, Eric.  Delta is used primarily in 
transmission systems, but many Munis and IOUs still utilize Delta 
distribution systems.  California is famous for it's Delta distribution 
systems.

Chris' explanation was for Wye systems.

There are advantages and disadvantages associated with both types of 
systems.  Each of you have for the most part identified correctly how each 
system is "wired".

As in most things, it is COST that determines the solution, given all other 
parameters are equal or nearly so.

Typically Delta systems are used where most of the load is in concentrated 
areas or the load requirements are for full three phase power.  The 
advantage is no 4th conductor (neutral) has to be installed (cost saving) 
with 3-phase distribution systems.  Load balance is achieved quite easily on 
a full three phase Delta distribution system.

That is why transmission is always Delta if it is operating AC.  Perfect 
load balance with no need for a neutral.  Today most all HV and EHV 
transmission lines are constructed with one or two static wires above the 
power carrying phase conductors.  The static wires are for that very 
purpose; to keep lightning off the phase conductors and NOT for carrying 
load current.

So the Delta system is a cost saver installation wise under these 
conditions.

Typically Wye systems are used where the majority of the load is NOT 
concentrated, or there is a large quantity of lightly loaded, long distance, 
rural single phase lines.  Load balancing is more difficult on Wye systems.

With a Wye system, single phase is run as a single "hot" wire and the common 
grounded neutral wire.  This can be done with one pole top insulator of 
proper rating and the neutral installed lower on the pole with little or no 
insulation.  To deliver single phase power a Delta system, TWO properly 
insulated phase conductors have to be run, most of the time with a Xarm and 
two insulators of proper rating.  This costs a LOT more on long runs to a 
single ranch home out in the boonies.

If the distribution is underground, then only one HV conductor with a 
concentric neutral has to be run.  With a Delta system, TWO phase conductors 
with appropriate insulation values have to be installed to deliver single 
phase service.  In high concentration areas, no problem.  But for long runs 
to single, small load services, it costs TWICE as much to do Delta vs Wye in 
conductor alone.

In single phase Wye systems, the common grounded neutral conductor IS an 
integral part of the circuit.  It carrys ALL the return connection to the 
substation transformer with exception of what might incidentally conduct 
through good ground.

So the Wye system is a cost saver installation wise under these conditions.

It would be best if a utility could use both types of systems together; that 
is Delta in the high density areas and Wye in the rural areas.  But the two 
systems are not compatible without transformer interconnection and there 
would be the safety factor of trying to remember which system you were 
working on.

So, typically you will not see Delta and Wye systems integrated in a 
utility's service area.

However, on the actual service side of distribution transformers you can and 
will find a mix of both Wye and Delta in a single distribution system. 
Again, the cost factor comes into play.

For example, even if a distribution system is Wye, for full, balanced 3 
phase loads (industrial pumping and irrigation pumps are two types of this 
use) a cluster of the single phase transformers will be connected in Delta 
across the primary and also connected Delta for the secondary.  This again 
is related to cost savings, both in the quantity and type of transformer 
that has to be kept in stock, and the amount of conductors that have to be 
installed to connect to the metering and the load.

Now back to the subject of the "loose" of "broken" neutral is a typical USA 
electric power homw service.  Since the neutral is derived from a center 
tapped winding on the distribution transformer secondary, and that neutral 
connection is required to provide the 120 VAC of the normal 120/240 VAC 
service, the loss of that connection produces the potentially damaging 
conditions some of you have explained.

Most foreign countries to the USA do NOT use the center tapped winding type 
of service.  They provide service across the full winding; that is 220 VAC 
up to 250 VAC.  There is no "neutral".

The advantage.  If you have a loose, poor or broken connection in either 
wire there is only a loss of service; not the "burn up appliances and pop 
light bulbs" condition that exists with the loss of neutral connection is 
the USA systems.

I trust this short explanation will shed a bit more light on some of the 
things that have been talked about.  It of course has nothing to do with the 
"Subject" of the thread.  Continue on with the GROUND ROD discussion.

Milt, N5IA