Transformers for mining excavators are special-purpose transformers. Their specifications are determined by special operating conditions and operating modes.
Mining excavators are very powerful loading machines (bucket- or continuous type) designed for mining works and loading of minerals. Loading is one of the most labor-intensive operations, its share in the drifting cycle is at least 30%.
Electric drives of excavator mechanisms may be of many types: from the simplest with asynchronous short-circuited engines to DC and AC drives with a wide range of control. But all of these drives have specific features with special requirements for power supply devices.
Power supply of mining excavators is provided by three-phase alternating current with a voltage of 6 kV. Excavators are in motion during operation. Therefore, their power supply is provided using a flexible cable (for tracked vehicles) or a three-phase contact network (for rail vehicles).
An important feature of excavator drives is a wide range of load changes — up to 40 times or even more. For the excavator drive, it is assumed that it can operate at a nominal rpm up to the maximum locking torque, after which the engine stops, but does not lose torque on the shaft. "Stalling" of the engine, that is, drop in rpm and decrease in torque on the engine shaft is unacceptable. This situation is possible when the bucket is working in the rock, if the bucket rests on fixed rock mass. Electrical resistance of the engine in the stop torque mode becomes minimal, while current passing through the stator circuits is almost equal to the starting current. Meaning 5-10 times or more higher than rated current of the engine.
The transformer through which electric power is supplied to the engine should be adapted to these temporary overloads. Frequency of such overloads for excavator drives is much higher than for other industrial drives.
By virtue of their design (air-barrier monolith), KPM transformers are better adapted to temporary overloads than dry transformers with cast insulation. And this determines their use in the power supply circuits of mining excavators.
Other features of transformers for mining excavators are related to their operating conditions. The transformer cannot be installed on a fixed solid base (due to its purpose), there are impacts and vibration. There is dust, dirt, and splashes in the quarries.
Transformers for mining excavators produced by KPM LLC have reinforced structure. Also they have specially designed cases for protection against adverse external effects.
KPM LLC has been successfully supplying transformers for crawler bucket excavators, which are the most common loading quarry machines. The volume of loading of rock mass by such machines is about 65% of the total volume of loading operations. At the moment, dozens of special transformers for mining excavators, mainly EKG-8 and EKG-10 types, have been produced and are in operation.