What Are Machine Ratings?

Ratings refer to the values specified for voltage, current, power, etc. of motors, steam turbines, hydraulic turbines, and other equipment under normal conditions. They are data that reflect the important technical performance of the product, and are used when producing, designing, manufacturing, and using the product. Technical basis.

Ratings refer to the values specified for voltage, current, power, etc. of motors, steam turbines, hydraulic turbines, and other equipment under normal conditions. They are data that reflect the important technical performance of the product, and are used when producing, designing, manufacturing, and using the product. Technical basis. Usually the most important data is engraved on the nameplate of the product, so it is also called the nameplate value. Ratings are divided into rated voltage, rated current, and rated power.

The rating is determined by the user and the manufacturer through consultation according to the needs of the user and the production technology of the manufacturer, and taking into account factors such as safety, economy, maintenance, and ease of use.

For a large number of products in the society, long-term social benefits need to be considered. The ratings are generally approved and published by recognized authorities on both sides. In China, the standards are issued by the Standards Division of the State Technical Supervision Bureau or related departments in a standard form. In these standards, items, definitions, requirements (such as allowable deviations), test methods, etc. of the rating are specified in detail.

The content of each product's rating varies depending on the usage.

The main ratings of electrical products generally include voltage, current, power, current type, working system, insulation level, ambient temperature, temperature rise, cooling method, etc. In addition, there are weight, volume (outer dimensions), insulation resistance, and withstand voltage strength.

For AC equipment, there are also requirements for frequency, phase number, power factor, and waveform. For the motor, there are torque, shaft center height, foot screw hole size, etc. It also has the ability to cut off current for switchgear.

Some of these ratings, such as the number of phases, must be guaranteed to be fully met. Some must be basically consistent, such as voltage, frequency (the allowable deviations are specified in the standard). Some must not be exceeded, such as current, power, torque. In addition, there are some special requirements, such as no no-load for DC series motors, no less than a certain value of the DC motor excitation current, no open circuit on the secondary side of the instrument current transformer. These requirements are specified in various electrical product standards.

Rating transformer

The operation of the transformer is divided into no-load (no load) operation and load operation. The operating conditions proposed by the manufacturing plant are called rated operation, and the conditions for rated operation are called the transformer rating.

Rated capacity-refers to the maximum apparent power of the secondary, expressed in volt-ampere or kilovolt-ampere.

Rated primary voltagerefers to the specified value of the voltage connected to the primary coil of the transformer.

Rated secondary voltage-refers to the voltage value across the secondary winding of the transformer when the primary winding of the transformer is connected to the rated primary voltage.

Rated current-refers to the specified full load current value.

The rating of a transformer depends on the construction of the transformer and the materials used. When using a transformer, it should not exceed its rating. ^[1]

Rating synchronous motor

(1) Rated power P _N refers to the mechanical power output on the shaft during rated operation, in kW.

(2) Rated voltage U _N refers to the line voltage applied to the stator winding during rated operation, and the unit is V or kV.

(3) Rated current I _N refers to the line current flowing through the stator winding during the rated operation of the motor, the unit is A.

(4) Rated power factor

Refers to the power factor of the motor during rated operation.

(5) Rated speed n _N refers to the synchronous speed of the motor

(6) Rated efficiency _N refers to the efficiency at rated operation.

In addition, the motor's nameplate also gives the rated frequency (the rated frequency of the three-phase motors produced in China are 50Hz), the rated excitation voltage, and the rated excitation current. ^[2]

Rating appliances

Maximum rated voltage rating requirements: 250 volts for portable single-phase AC and lightweight DC appliances; 440 volts for all other appliances.

Compliance is checked by inspection marks.

• This requirement of this standard is based on the assumption that the voltage between the power line and the ground line does not exceed 254 volts during normal use.

• Increasing the limit of the specified rated voltage is under consideration. ^[3]