Harris Gates Five 994 9204 002, Техническое руководство

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clearly show that the voltage regulation of
an unbalanced system is poor.
2.4.1.4.
Three Phase Delta Distribution
Transformers
Figure 2-1 shows open and closed delta
systems. The closed delta impedance look-
ing into each terminal (A, B & C) is exactly
the same; but this is not the case in the open
delta configuration. Depending on the im-
pedances of the transformers in the open
delta circuit, line voltage unbalance suffi-
cient to impair satisfactory operation of the
overall transmitter may result. For this rea-
son, along with their inherent susceptibility
to transients, Harris does not recommend
the use of open delta systems.
The only advantage of the open delta is
lower initial cost, and this is partially offset
by the fact that when only two transformers
are used, they must be larger than the three
transformers in a closed delta system.
Difficulties have often been experienced
with open delta systems; but when a third
transformer was added to close the delta, the
problems disappeared.
There is another problem which can occur
with an open delta system, and that is
caused by lightning and switching tran-
sients. When lightning strikes or heavy
loads are switched on a power distribution
system, high voltage transients are propa-
gated throughout the system. Unbalanced
impedances will enhance these transients
and can cause transmitter damage, particu-
larly to solid state rectifiers.
Many transmitters are located at the end
of a long transmission line which is highly
susceptible to transient phenomena. De-
vices such as Metal Oxide Varistors are
inexpensive and very effective in reducing
over voltage spikes. These units are limited
in the amount of energy that can be dissi-
pated, but will handle, if designed properly,
very large currents. You can’t take a direct
lightning hit and still operate, but not many
things will. It has been reported by engi-
neers that installation of a third transformer
and transient protection devices, have
eliminated the difficulty.
2.4.1.5.
Three Phase Wye Distribution
Transformers
The WYE connected system is also con-
sidered a symmetrical form of three phase
power distribution. All impedances are bal-
anced as seen from each terminal (see Fig-
ure 2-2). It is important when using a WYE
connected system that the fourth wire (neu-
tral) is connected to the mid-point of the
system as shown in the diagram. When this
connection is made it provides a path for the
zero sequence currents as well as any har-
monic currents which are generated due to
the rectification of the secondary voltages.
Today, many transformers are supplied
with all of the primary terminals available
so that either a delta or WYE connection can
be made. Table 2-1 shows the different line-
to-line voltages that are available with this
configuration.
In summary, both symmetrical power dis-
tribution systems are satisfactory because
of their balanced impedances. Use either a
closed delta or a four wire WYE system for
maximum transmitter performance. Never
use an open delta system just to cut costs -
it could cost dearly in the long run.
2.5.
General Installation
Requirements
The key to a rapid and successful setup is
careful planning prior to delivery of the
system. HARRIS offers, as an option, engi-
neering services to review and comment on
proposed installations. In addition HARRIS
offers, as an option, design, fabrication, and
installation services to any required level
for total integration of the system into a
facility.
2.5.1.
Equipment Placement
The transmitter should be located to per-
mit adequate maintenance access and suffi-
cient ventilation. Primary AC power cables
can enter the transmitter at a variety of
locations and the specific location of entry
will need to be determined on site. The
grounding strap between the transmitter
and the station earth ground must be prop-
erly connected before AC power wiring is
attached to transmitter.
2.5.2.
Pre-Installation Inspection
Prior to performing the installation of the
GATES Series™ transmitter, it should be
thoroughly inspected for any connections
which may have loosened during shipment.
Figure 2-1. Three Phase Delta
Distribution Transformers
Figure 2-2. Three Phase WYE
Distribution Transformers
Delta connected
transformer
WYE connected
transformer
210 364
220* 380*
230 400
240* 415*
250 433
* Typical voltages in some areas of the
world.
Table 2-1. Typical Line Voltages
Delta or WYE
Lifting Equipment
(Fork Lift, etc) 900 lbs (408 kg)
capacity
Hand Tools For opening wooden
crates
Shims (2" by 2") Aluminum, assorted
thicknesses
H a n d O p e r a t e d
Hole Punch
For adding 0.25"
hardware holes to
0.020" thick copper
g r o u n d s t r a p a t
transmitter ground
connection.
Table 2-2. Special Installation
Tools and Equipment
Transformer, Low
Level, A20T01 472 1678 000 (1)
T r a n s f o r m e r ,
Power, A19T01 See packing list for
part number
Table 2-3. Equipment Supplied with
Transmitter and Listed on Packing
Check List Supplied with Transmitter
2-2 888-2314-001 Rev. AC: 2/29/00
WARNING: Disconnect primary power prior to servicing.