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How To Wire a MEP002A or MEP003A Diesel Generator

This article describes common power  generation connections and discusses the use of power transformers.  This is a scanned article and there may be typos and some odd images. We tried to scan and convert this so that it is more accessible on the Internet.  Please see all the figures and pictures at the end of the text portion.

You can also download the original article written by Kenneth  Tollstam,  Jr.  Mr. Tollstam served four  years in tactical Signal battalions  in Europe.  He  has  also  served  as  the  OIC of  an electronics maintenance shop and as a C-E commodity manager for the  9th   Infantry   Division   where  he  was  promoted   to   W02. Tollstam holds a B.A. from St. Martin’s College in Washington. He recently separated from the Army.  We would like to thank Mr. Tollstam for his insight and help in educating folks on military generator wiring and electrical theory.  As always, please consult a licensed electrician before attempting any electrical work.

Download Original File Here: How-To-Wire-A-MEP002A-or-MEP003A-Military-Diesel-Generator

COMMON POWER GENERATOR CONNECTIONS

Some technical manuals for both communications assemblages and power generation equipment are vague in their instructions for connecting the power cables to the load terminals. The technical manuals for the power generation equipment do not give any guidance for connecting the equipment grounding conductor, EGC.  These  generators were designed  to power many different  kinds of equipment, not just communications equipment, and it is the user’s responsibility  to  configure  the  generator  to  supply   the proper  kind of power. The following will explain in detail the basic connections to be made to the common generator sets (gasoline / diesel   DOD models)   currently in use   by the military.

The gasoline driven 3 K w, S K w, and 10 K w generators are designed so that they can provide the three kinds of power described earlier at the turn of a switch. The diesel driven  IS Kw, 30 Kw, and  60 Kw generators are usually  operated to provide  3 phase,  120/208  volt, 4 wire power  into  a central distribution system.  The gasoline driven 3 Kw and  5K w generators are usually used to provide single phase, 120 volt, 2 wire power for communications assemblages. Bothe types of generators operate basically the same.  When the generators are providing single phase, 120 volt power, they provide a balanced output as illustrated in figure 9.

Between either   load   terminal   and   ground, there   is a potential of 60 volts.  Between both load terminals (across the full phase) the full 120 volt potential is present.  This can put a potential difference of 60 volts between the neutral return line and ground. This can be a source of noise to some types of communications equipment. This floating power source does not provide a neutral. If connected  improperly, there  will be no low  resistance  third  wire, EGC,  ground  to system ground (power  source  neutral), since there is actually no system ground. This can be potentially hazardous in that if a ground   fault (short circuit) develops anywhere in the system, it will not clear (trip the circuit breaker or blow the fuse). Incorrect methods of connecting to this type of power source  can  create  many  kinds  of undesirable situations to include  having  a  60  volt  potential  between  the  generator frame  or  trailer  and  the shelter.

Figure  10 shows  the  proper   way to connect the  power cable   to  the  load   terminals  of  a  gasoline   driven   3  K w generator, model  MEP-Ol6A (or  the load  terminals of the generator switch  box  on  the  trailer)  for  single  phase,  120 volt, 2 wire operation. Make sure the switch (Sl) in the generator  control  box   of   the   generator  (or   on   both generators  for a trailer  mounted set) is adjusted to the 120 volt,  single  phase  position.

The white conductor (neutral return) and green conductor (ground, EGC) should be connected to Ll as illustrated. Additionally, a  6  or  8  A WG  insulated   conductor (wire) should  be connected between  L I   and the generator or trailer ground  which in turn  should  be connected  to earth  ground. Remember, LO  is not  ground. The  black conductor (“hot” line) should  be connected to L2. Wiring a single phase,  120 volt, 2 wire primary  power this way unbalances the output  of the generator and  gives a power source  neutral.  See figure 11.

Connecting the ground line, EGC,  to the system ground (power    source    neutral)    keeps   the   potential   difference between neutral and ground  to zero, or near zero, volts. This also  provides  a low resistive ground  back to system ground (power  source  neutral) at the generator as discussed earlier.

The  principle   behind  the  single  phase,  120 volt,  2 wire power connection to  the gasoline  driven  5 K w generator is the same as that  for the 3 K w generator except  that  the load terminal   connections  are  different.  Figure   12 shows  the correct   single   phase,    120  volt,   2  wire   primary    power connection to a 5 K w generator, model MEP-0 17 A. Again, insure that  the phase selector  switch inside the control  panel is set to the  120 volt,  single  phase  position.

Sometimes the gasoline  driven  I 0 K w generator is used to provide  single  phase,  120  volt,  2 wire  power.  Again,  the power cable connection principle is the same as for the 5 Kw and  3 K w generators, except  the load  terminal  connections are  different.  Figure 13 shows  the  correct  primary  power connection  for   single   phase,  120  volts   from   a   10  Kw generator, model  MEP-003A. Insure that  the  phase  selector switch  inside  the  control panel  is set  to the  120 volt,  single phase  position.

The  10 Kw generator is often  used  to supply single  phase 1201240 volt,  3 wire  power. Other types  of generators can also provide this  type  of power. When  this  type  of power  is required,  the phase  selector switch  in the control panel  must be set to the 1201240  volt,  single  phase  position. The  output from the  load  terminals will be as  illustrated in figure  14.

When  dealing with  single  phase, 120 volt,  2 wire  power cables  with  a  third   wire  grounding conductor,  the  color coding is almost always consistent: black for “hot”, white for neutral  and  green   for  ground.  When   dealing with  multi­ phase or single  phase, 3 wire power  cables, the color  coding may differ  from  cable  to  cable. Usually  the  cable  will still have a black conductor which  will represent one of the “hot” lines. The  other  “hot” lines for the  remaining phases  may  be colored  red,  blue,  yellow  or  green. The  color green  is now used only for the ground conductor but  in some  of the older cables  this  may  not   be  the  case.  Figure  IS illustrates  the proper  way  to  connect a standard  military single  phase, 3 wire, 1201240 volt  power  cable  (issued  with  the  ANITRC- 112 Radio  Terminal Set)  to a gasoline driven, model  MEP-003A, 10 Kw generator.

Note:  The  red and  black “hot” wires may be transposed. Remember  that    Lo   is  system  ground  (power  source neutral) and  not  ground. The  ground and  neutral wire must be connected together on  Lo and  an additional wire must  be added    between  Lo   and   earth  ground.  This   insures  the connection of  Lo  to  ground. Be sure  always to  check  the pertinent  technical  manuals  before  making any   primary power  connections with  an  unfamiliar power  cable.

Connecting to 3 phase, 4 wire power  is basically the same regardless  of  the   power  source.  Almost  all   military  AC power  generators are capable of providing 3 phase, 120 I 208 volt,  4 wire power, and  the connecting procedure is the same. The  color coding from  power   cable to  power   cable   may differ, so  be sure to  check   the  technical  manual.  Figure 16 illustrates the  proper way  to  connect to  3  phase, I20I 208 volt,  4 wire  power.

The  neutral wire  will probably be white.  The  ground  wire may or may  not  be present. lf it is present, it will probably be green  or  bare.  Again, the  neutral and  ground conductor (if present) must  be connected together to Lo,  and  Lo must  be connected to earth ground to insure the ground connection. When  dealing with  10 Kw,  30  Kw,  and  60  Kw generators, make  sure   they  are  configured  to  supply I 20 I 208  volts  as these   generators are  capable of  supplying 240/416 volts. Check the  technical manual.

POWER  TRANSFORMERS  FOR   PRIMARY  POWER

In  Europe  where  the  standard  commercial power  is 3 phase, 220(380  volt, 4 wire, it is sometimes necessary to use step-down  power  transformers to  operate equipment designed  to operate at 120 volts. The 3 types of transformers commonly used are the single phase autotransformer, the single  phase  isolation transformer, and  the 3 phase, 4 wire wye transformer. Most  transformer power ratings are given in kilovolt amperes (K VA) and  the load calculations are the same as  those  for  power  generators.

A good  example of a single  phase auto transformer is the TF-167.  See figure  17.

Be very careful  when connecting an auto transformer to an electrical power source. On the input side of the transformer, make certain that  the “hot” line of the input  is connected to the top of the transformer coil (terminal Z in figure 17). If the “hot” and neutral lines on  the input side of the transformer are transposed, there will still be 120 volts across the output; however,  the neutral line will carry a 220 volt potential measured  to ground all through the equipment connected to it. See figure  18.

This  can  create  a very dangerous situation. This actually caused  a  multiplex unit,  TD-754 / G,  to explode. The  TD-754/G has  an  AC  input  line filter,  as does  most  military electronic equipment. The  filter  has electrolytic capacitors between   both   sides  of  the  line  (“hot” and   neutral)   and ground. Having  a 220 volt  potential between  neutral  and ground   caused  one  of the electrolytic capacitors to  break down  and  violently  explode. This  explosion caused  major damage   to  the  equipment, bending  the entire  case  out  of shape.  The  equipment was not even  being used nor  was it turned  on; it was merely plugged  into the power receptacle.

The   correct   way         to    connect   a    single   phase autotransformer, such as the TF-167,  for supplying primary power is illustrated in figure  19.

Another commonly used transformer is the single phase isolation  transformer as illustrated in figure 20.

With  this kind of transformer, there are the same kind of floating power output problems as are encountered with the single phase 120 volt output of a power generator. Figure21 illustrates the proper  way to connect  a single phase isolation transformer for  primary  power.

The last kind of transformer normally encountered is the 3 phase, 4 wire wye transformer as illustrated in figure  22.

The output  of this kind of transformer is the same as the 3 phase, 4 wire  output of a  power  generator, and  the  load should be connected   in the same  manner.

When dealing with power transformers, there may not be any technical  r:anuals available  to refer to for information. Most transformers have  a  data   plate  which  will give the voltage  and   power   ratings   and   show   the  line  and   load terminal  configurations. Always  make  sure  that  the transformer   to  be  used  will  operate on  the  line  voltage available,  will  supply  the  voltage  needed,  and  will adequately   handle   the  load.   An  unfamiliar transformer without descriptive information, either  on the  transformer or elsewhere, should  be left alone.

The frequency of the line current, whether it is 50 or 60 Hz, will  generally  not   affect   the  operation  of  most  military electronic equipment. Most  of the power generators used m the military can supply  both  50 and  60 Hz. A transformer will supply the same  frequency  at the output that  is applied

to the input.  Because inductive  reactance  is more efficient at higher frequencies,  some  inductive  devices, such as electric motors  and  transformers, designed  to operate at 60 Hz may overheat when operated at 50 Hz. Inductive electric  motors will also  tend  to  rotate  slower at 50 Hz than  at 60 Hz. It is important to check  whether  or not the inductive equipment is  rated  to  operate at  the  line  frequency  available. If the equipment  will  only  operate at  60  Hz  and  the  only  !me frequency  available  is 50 Hz, as is the case in Europe, then a rotary power converter will be necessary.  A rotary  power converter consists  of an electric  motor  which turns  a power generator. The 50 Hz line current powers the electric  motor which  turns  the  power  generator which  produces a 60  Hz power   output.  The   same   rules   that   apply. to the  load connections and  calculations of standard military  power generators also  apply  to  rotary  converters.

Though not all the aspects  of primary  power distribution have   been  covered   in  detail,   this  article   offers   a  baste foundation from which to work. Primary power considerations are vitally important to safety,  both personal and equipment. Electric power must be treated  with respect. The  harnessing of electrical  energy  has been the single most important influence  on  our  highly  society.When electricity   goes  to  work   for  us,  every  btt  of  1t   must   be controlled. Loss of control can  result  in injury  or death.

Primary    power   considerations  are   also   important  to quality,  dependable telecommunications. No less planning should  go  into  primary  power  than  goes  into the establishment of systems  and  circuits.

REFERENCES

TM  11-486-7 26 Apr  63 Electrical Communications Systems Engineering   Power

FM  55-506-1  22 Apr  77 Basic Electricity

TCII-6    Sep  76 Grounding Techniques

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