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The Excitation System and AVR Working Principle of the Stanford Generator

Aug 25, 2023 | Technical Literature | 0 comments

Headquartered in the UK, Stamford Generator is a 100% holding subsidiary of Cummins Corporation. It is the world’s leading and leading manufacturer of alternator technology. AC 4-pole 5KW-3000KW generators occupy more than 30% of the world market. It has production plants in the United Kingdom, India, the United States, Indonesia and China. Sri Lanka Fu Generator is manufactured in accordance with various international standards in accordance with the requirements of the international standard S09001. Among them, the factory located in China is Cummins Generator Technology (China) Co., Ltd., and the factory is located at No. 49, National High-tech Industrial Development Zone, Wuxi, Jiangsu Province. piece.

Pressure regulation performance requirements

There are many types of Stanford generators, including single-phase or three-phase, four-stage, single-point or double-point, land use or marine use, and other specifications. You can choose a suitable generator according to your actual street conditions. Generators are usually composed of stator rotors, end cover brush bases, bearings and other components (the appearance is shown in Figure 1). Under the worst circumstances, the new Tanford generator can provide extremely reliable power as a main power source or a backup power source.
The alternator driven by the engine whose speed regulation characteristics meet the requirements, together with its excitation system, should be able to maintain its stable current under the condition that the load ranges from no-load to rated load and its power factor is a constant value. The change value of music is within +2.5% of the frontal voltage. Emergency generators can be within 3.5% of soil.

When the load of the alternator is no-load, the speed is the rated speed, and the electric music is close to the rated value, when the symmetrical load of 60% of the rated current and power factor is not more than 0.4 is suddenly added and unloaded, when the voltage drops When the voltage rises, its transient voltage value should not be lower than 85% of the rated voltage; when the voltage rises, its transient voltage value should not exceed 120% of the rated voltage, and the voltage is restored to within 3% of the final stable value. The time should not exceed 1.5s. The time required for the emergency generator voltage to recover to within 4% of the final stable value may not exceed 5s.

Excitation system and voltage regulation method

1. The stator of the main generator controlled by the self-excitation AVR provides the excitation source for the magnetic field of the exciter through the SX440 (or SX421) automatic voltage regulator. The automatic voltage regulator, referred to as AR, is a control device for adjusting the carbon excitation current of the magnetic field of the exciter. The AVR reacts according to the electrical response signal from the stator winding of the main engine, and controls the excitation field of the exciter at the same time, and adjusts the rectification output power of the exciter motor, so as to meet the requirements of controlling the magnetic field current and the excitation of the generator. The system and pressure regulating system are shown in Figure

2.

(1) SX440 adjustment board
AVR senses the average voltage of the two phases to ensure a relatively local voltage adjustment rate. In addition, it also monitors the engine speed. If it is lower than the pre-selected speed (HZ), it will reduce the output voltage accordingly to prevent engine failure at low speed. Over-excitation, reduce the impact of loading to reduce the burden on the engine
(2) SX421 pressure regulating plate
In addition to the features of the SX440 voltage regulator board, it also features three-phase rms sensing, which also provides overvoltage protection when used with an external circuit breaker (mounted on the switchboard)

3. AVR accessories
If the built-in circuits of SX440, SX421, MX341 and MX321 series automatic voltage regulators are connected with accessories, the generator can be controlled under “droop” or “no static difference”, AVR (no power)/PF (power factor) control Parallel operation; MX321 automatic voltage regulator can also provide short-circuit current limit control.

Working principle of permanent magnet generator

When the generator is working, the stator of the permanent magnet machine outputs P2, P3, and P4, and the voltage value is about 130-150VAC. After rectification, output X, Xx (approximately 8-9VDC at no-load) to the stator wire of the electric ball, and the rotor wire of the exciter induces alternating current, which passes through the 6 diodes installed on the rotor wire of the exciter. The DC is rectified, and the DC current is sent to the main rotor coil. The main rotor coil generates a magnetic field in the rotating state, and the main stator coil induces an alternating current (such as 400VAC output).
When the load increases or decreases between the foreheads, the output voltage U,, W of the generator will increase correspondingly between the peaks and lows, P6, P7, and P8 are half of the 400VAC output (tap electricity), and P6, P7, and P8 are reversed to For the AVR board, if the load increases, P6, P7, and P8 will decrease at the moment the load increases, and the AVR board will automatically increase the output values of X and xx to increase u, V, and W to 400VAC.

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