Hello,
We are installing a customer-owned 25 kV to 4.16 kV substation. This is a skid mounted system, and the only exposed energized parts are the tips of the high side transformer bushings. The substation will be outdoors, and will be protected by a 7 foot high fence with a locked gate.
Table...
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I work for an electrical contractor, primarily in the mining and gas industries. A customer installs and maintains their own 12,470 volt power distribution system. They use wooden poles with a cross arm that holds the three phases. There is also a single wire at the top of the pole...
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We are in the very early stages of doing the electrical engineering on a pump project. The pumps will be used to pump water over a long distance (not much lift) for a gas processing operation. The people that engineered the hydraulics say that they need three 600 horsepower motors to do...
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Underground coal mines use large electric motors to operate their ventilation fans. The number of fans required depends on the size and depth of the coal mine. One fan, in particular is a 2000 HP, 4kV, 890 rpm motor that is started directly across the line. The motor has two vibration...
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We have an elevator application that uses a low speed (55 rpm), 100 HP DC shunt wound motor. We have a lot of problems with contactors in the shunt field circuit that fail. These contactors are being used for required testing purposes. The contact tips burn severely when the...
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I have a question regarding the partial replacement of parallel conductors feeding a three phase, 200 HP, 575 volt motor.
The original installation used parallel 500 kcm aluminum cables that were 1800 feet long. The cables were damaged and were going to be replaced with parallel...
To all,
We have a customer that has a 12,470 volt, three phase, resistance grounded power system. The secondary of the source transformer is wye connected. The neutral grounding resistor resistor limits the line to ground fault current to 15 amperes. They want to install two single phase...
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Is this possible:
At one of our customer's mining substations, they operate 2 -10 MVA transformers in parallel. The transformers are 69 kV primary (delta) to 12.47 kV (resistance grounded wye). At some point in time, the center fuse on one of the transformers (T1) blew. The fuse size...
To All,
A contractor is installing a single phase 120/240 volt service supplied by a small (25 kVA) indoor 480 Volt to 120/240 Volt transformer at one of our sites. From what I understand, that is considered a separately derived system by the NEC. As such, it much have a system bonding jumper...
All,
I work for the Mining Industry. All of the three phase power that is delivered to the underground area of the mine is resistance grounded. The grounded side of the neutral grounding resistor (15 ampere limit) is connected to a safety ground bed that must be located 25 feet (minimum) away...
I work for a small electrical contract company that does custom design and construction of control panels for use primarily in the mining industry. The regulations governing electrical installations used in and around a coal mine are very well known. One of the hazards associated with coal...
When installing an oil filled 10 MVA transformer - 69 kV to 12.47 kV with lightning (surge) arrestors mounted near to the bushings, should the incoming (outgoing) leads be:
a) connected directly to the bushings with a tap going to the arrestor;
b) connected to the arrestor and continue through...
As is required by underground coal mining laws in the US, any three phase power that goes underground must be resistance grounded to a safety ground bed located at least 25 feet away from the substation ground bed. The typical value of the grounding resistor is either 15 or 25 amperes. The...
I have encountered a situation with a resistance grounded system that has a 25 ampere neutral grounding resistor. There is a 25:5 CT in series with the resistor to measure ground fault current. The CT secondary is connected to three CO-11 relays that are connected in series using 300 feet of...
