[Heathkit] Line voltgage

[Gerry Steffens]

To the contrary, Mike it sounds like things in Fort Wayne are right on the
mark.

The mechanical tap changing equipment in distribution substations relies on
mechanical tap-changers-under-load to physically change the voltage in 5/8%
steps.  That amounts to about .75  volts per step on the 120 volt base.
Consider that to keep the equipment from continuously hammering itself to
death under continual change everytime someone flips a switch or two,
normally the solid state controls on voltage  regulators or load tap
changing transformers are set for a deadband of about plus or minus 1.5 to 2
% (3% to 4 % total).  This is done to save dollars.

A municipal utility in the state of Washington advertised close voltage
regulation in the name of power quality and set its equipment to hold  with
less than 1 % deviation.  They did it somewhat successfully for about 18
months.  Then the hardware which is slated for about 20 or more year life
died.  Not just one but within a few months almost all of their units had
worn out tap changers.  A couple blew up because of the failures.  Both as a
safety and an economic measure, you do not want to pay the costs to maintain
any tighter bandwidths than about 3 to 4 percent.  This is manufacturers
spec on most all voltage regulating equipment.

A typical setting is to set the target voltage at 119 and then set the
bandwidth around it to be plus and minus 2 volts.  121 to 117.  Yup seems
about right to me.

As things operate today, unless you are connected directly to a generator
with no transformation between you and it, there are no affordable ways to
provide continuously variable voltage regulation.  If connected to a
generator the exciter of the generator can be controlled to provide constant
voltage.  Power plants are operated that way (constant voltage at the
generator terminals.  Now consider millions of customers connected to a near
infinite grid of transmission.  A difficult chore to operate, more so today
than in times gone by.

As I said previously, I've been a utility engineer almost as long as I have
been restoring these glowbug things.

Just thought you might appreciate how it works.

73

Gerry


Collecting & Restoring since 1959
Gerald Steffens P.E.
Rochester, MN