What Is a Submersible Motor?

A submersible motor is a motor specially developed for underwater use. It is a motor that is directly connected to the pump and runs in the water. The motor is used for various types of submersible pumps, which are integrated with the pump and run for a long time in the sewage of various water quality. The harsh working environment determines that its sealing structure is greatly different from conventional motors.

With the increasing demand for submersible pump flow and head in the market, the power of the supporting motors has gradually increased. For example, it is still driven by low-voltage motors, and the corresponding large currents and cables also follow. The weight of the cable itself brings great inconvenience to its wiring and fixing, and the increase of the cable also adds difficulties to the sealing of the outgoing cable.

The submersible motor is produced according to the GB / T 2818-2002 standard. It is mainly divided into four types: oil-filled, water-filled, dry, and shielded.

1. The oil-filled submersible motor is filled with mechanical oil inside, and is supported by rolling bearings at both ends. The upper part uses hard alloy as a mechanical seal. It can be used in large occasions containing mud and sand, and it can also be used for tilting and horizontal use.

2. Water-filled motors are divided into ordinary submersible motors and special submersible motors. The main wear-resistant parts are made of imported materials (guide bearings, thrust bearings, etc.). It has the characteristics of high thrust resistance and high wear resistance.

3. Dry-type submersible motor, dry-type motor, the inner cavity is filled with air, similar to the land motor, and the structure is simple.

4. Shielded submersible motor, the stator of the motor is made of non-magnetic stainless steel thin-walled shielding sleeve, end ring and casing. The sealed chamber is tightly closed and filled with solid filler. ^[1]

This is a submersible motor specially designed for supporting pumps for pumping groundwater. Due to the diameter of the wellhead, the outer diameter of the motor must be limited. Therefore, it adopts a slender structure. The commonly used varieties are 100, 150, 175, and 200. , 250, 300, 400 series, with power ranging from 0.75kW to 410kW. Most of these submersible motors are water-filled, that is, the interior of the motor is filled with clean water.

Because the motor is applied in mines, rivers, and swamps, there are no excessive size restrictions on the motor. According to the combination with the pump, it can be divided into shaft extension up type and shaft extension down type.

In addition, according to the material filled in the motor, it will be divided into the following types:

a. Water-filled: Fill the inner cavity of the motor with clear water.

b. Oil-filled: The inner cavity of the motor is filled with oil with insulation and lubrication properties.

c. Dry type: Enclose air or other protective gas inside the motor. Among the various types of submersible motors mentioned above, the differences from general land motors are the insulation method, bearing structure and sealing method. The characteristics are summarized below.

Because this type of motor is full of water inside, it is widely used in deep wells for water extraction, coal mine drainage, general water supply pipes and pumping devices in construction equipment. This motor is unique in its insulation method and bearing form.

1. Water resistant insulation

There are several types of water-resistant insulation:

a. Water-resistant insulation wire

The winding is an electromagnetic wire made of plastic material with good water resistance covered by general copper wire, that is, the electromagnetic wire itself is used for insulation. The materials used for insulation are polyethylene, polyvinyl chloride, and polytetrafluoride. In recent years, Polyvinyl chloride has rarely been used. Generally, polyethylene winding wire is used at normal temperature 20C water temperature, cross-linked polyethylene type is used at 60-80 water temperature, and PTFE winding wire is used for high temperature water type.

b. Water-resistant insulation

The stator winding is made of water-resistant insulation resin to protect the electrical part of the motor. It is especially suitable for small submersible motors. The water-resistant insulation resin must meet the following main technical conditions:

(1) Low hygroscopicity;

(2) Good adhesion to structural parts.

(3) No adverse effects on the materials of other structural parts.

(4) It can expand or contract with the windings and other components. In view of the above requirements, it is considered that the use of epoxy materials is ideal.

c. shielded

It was originally a submersible motor developed for the chemical industry and the use of atomic energy. However, with the improvement of the production level, it has also been selected in many small displacement motors in recent years. It has now become a drag A general-purpose submersible motor for deep and shallow well pumps. The structure is provided with an extremely thin cylinder called a shield sleeve on the inside of the stator, in order to protect the electrical part of the motor. Its insulation from water depends on the motor casing and the shield sleeve. The heat-resistant insulation is carried by insulating materials such as epoxy resin filled in the interior. The electrical part of this motor is not in direct contact with water. This is very different from the previous two types. In this type of motor, ordinary enameled wire is generally used as the winding wire, and the shield sleeve uses an austenitic stainless steel material with a thickness of about 0.15-0.25 to reduce the eddy current loss in the shield sleeve. Due to the existence of the shield sleeve, this motor The air gap is larger than that of other types of motors, so the power factor is affected.

2.Water lubricated bearings

In water-filled submersible motors, the bearings are lubricated by fresh water filled inside the motor. Because water is different from general lubricating oils, its lubrication effect is very low, and it has reached a critical lubrication state. Therefore, as a bearing, it is necessary to choose a structure and material that cooperate with water, especially thrust bearings. The huge impulse produced has a relatively large bearing capacity. In this way, it is not only beneficial to the motor itself but also to the submersible electric pump. Therefore, various types of bearing structures and materials have been developed successively.

a. Guide bearing

Also called bearing bush, it plays the role of righting the rotor in the motor. The force is smaller than that of thrust bearings. At present, there are a variety of materials, including tin bronze, graphite, Ferobestos composite material, FM, etc. Copper bearing bushes are used in the structure. Draw three straight grooves, graphite and Ferobestos bearing bushes, and add two spiral grooves inside to enhance the cooling effect. One bearing bush is usually used on one side of the low-power motor, and the high-power motor uses a double-watt structure with spiral fingers that are paired forward and backward.

b. Thrust bearing

Thrust bearings are divided into two types: integral type and block self-aligning type. Integral type is used for low-power motors, mainly used in 100, 175 series, 200, 250 series low-power motors. The skateboard is quenched with 3Cr ₁₃ and the thrust is DAP, D23 and graphite, polytetrafluoroethylene. Compared with DAP plastic, Many, its advantage is low price, which is convenient for mass production.

The block self-aligning structure is used for motors above 200 series. Its load bearing pressure is much higher than that of the integrated thrust bearing. The manufacturing process is also more complicated. There are two forms of abrasive materials commonly used. One is stainless steel versus graphite. It is used in motors with higher power. Second, Ferobestos uses tin bronze. This is the most commonly used method.

In principle, it is inappropriate to use a water-filled submersible motor in an environment with poor cooling conditions. At this time, an oil-filled submersible motor should be used. Submersible motors used to drag sewage pumps used in buildings and sewage discharge equipment. Because the motor casing is buried by attachments, the load changes, etc., the stator windings should use enameled wires with heat and humidity resistance, and sealed in the motor. Insulating material with good heat resistance to prevent surrounding water from entering the inner cavity of the motor. In this kind of motor work, sometimes all work in water, and sometimes the water surface may be exposed. Therefore, in order to prevent the motor temperature from rising too high, a temperature relay is installed in the motor, which cuts off the power when the temperature inside the motor is too high.

The selection of the shaft seal in this motor is as important as the selection of the insulation method. The water pumped by the pump is various. In order to effectively prevent water from entering the motor from the motor shaft extension, mechanical seals are generally used. It is important For the sliding parts and sealing materials, it is necessary to choose a material suitable for the discharged water. The bearing is generally a rolling bearing. It is lubricated by the sealed oil. At the same time, it must be able to bear the axial load. Five dry submersible motor

In building construction, the submersible motors used for pumping and drainage are usually mobile and used under harsh conditions such as pumping and discharging mud water. Therefore, the motors required to be manufactured are light and convenient for maintenance and inspection, and have relatively High heat resistance. For this reason, the motor is dry (not filled with water or oil), with B or F insulation, and a temperature relay is usually installed in the motor. Stop.

1. In the case of large sand content in the well, special attention should be paid to the operation of the pump until the water in the well is not turbid, so that the pump can be stopped. Otherwise, the sand will stop collecting on the rear cover of the impeller, and the pump will not start when it starts again. Further operation will burn the motor. This phenomenon often occurs when the wells are not thoroughly washed in the market. At this time, the motor must be operated until the water in the well is not turbid, and then the machine can be shut down.

2. The insulation resistance of the stator winding of the submersible motor is zero, but the electric pump can still operate normally. This phenomenon can only occur on star-connected submersible motors. When the star point of the motor is not well wrapped, the insulation of the stator windings to ground is zero, so although the motor appears to be grounded, some abnormal phenomena such as increased motor current will not occur. The electric pump can still operate normally, but it cannot meet the electrical Requirements for safe operating procedures. In this case, the electric pump should also be taken out of the well for disassembly inspection, the star point should be re-wrapped, and the insulation resistance value of the stator winding of the motor should be raised above the specified value, and then put into operation again ^[2] .