Discussion on the Application of a Technical Scheme for Electric Locomotive Transformation

summary:In this paper, the main problems of the old electric locomotive, through the use of a new type of DC fast circuit breaker, DC microcomputer integrated protection device and DC electromagnetic contactor on his transformation, improve the reliability of equipment operation, to ensure the safety of production, while saving business investment, is a worthy of a wide range of technical solutions in the national industry.

:DC fast circuit breaker, DC microcomputer comprehensive protection, DC electromagnetic contactor, safe production, saving investment

1. Overview

At present, the German EL1(150T) and EL2(100T) electric locomotives of the Ministry of Transport of Bengal Steel have been in use for more than 30 years. The electrical equipment technology adopted has been very backward, and the equipment has poor reliability, even causing many major accidents of vehicle fire and combustion. Due to the frequent occurrence of vehicle accidents, it has brought serious impact on production, and also led to a substantial increase in operation and maintenance costs. The root causes mainly exist in the following aspects.

1) The old-fashioned DC fast circuit breaker protection setting value is very discrete. With the passage of running time, the over-current tripping parameter often deviates, which is easy to cause misoperation or rejection, and the parameter correction is very troublesome;

2) The vehicle fault often causes the circuit breaker of the superior power supply station to trip, resulting in the power supply fault of the whole line;

3) When a short-circuit fault occurs at the remote end of the vehicle, the fast circuit breaker often does not trip, which may easily lead to serious accidents such as locomotive burning;

4) The rubber cup of the electric air contactor is easy to age, resulting in poor coordination with the cylinder and air leakage, resulting in equipment failure.

In view of the above reasons, we have carried out extensive market research on electrical equipment in the domestic DC traction market. Through research, it is found that with the continuous development of new materials and new technologies, new products and various application technology solutions are constantly being introduced, and the products currently used in our vehicles are already obsolete products. In this case, we have communicated with the equipment manufacturer for many times on the technical plan. In 2011, we tried to transform an accident car, and the effect has been very satisfactory so far.

In the technical scheme of transforming EL2(100T) electric locomotive, the fast circuit breaker adopts QDS8 series new DC fast circuit breaker, and is equipped with ST700 series DC microcomputer integrated protection device to replace the electric air contactor with WLCZ1 series DC electromagnetic contactor.

1. New type of DC fast circuit breaker

The QDS8 series DC circuit breaker selected for this transformation is a single-pole, non-polar fast circuit breaker with a rated working voltage of DC 1800V and a rated working current of 1250A.

1) Compared with the old fast circuit breaker with complex structure, QDS8 series products are modular in structure, mainly composed of contact system, closing and holding device, direct overcurrent instantaneous release, arc extinguishing system and auxiliary contact. The structure is very simple, which is very convenient for disassembly and maintenance. And the use of side arc, arc safety distance up to 90mm, is conducive to the installation of small space;

2) Since the DC power supply has no zero crossing point, the contact system is seriously damaged when the DC fast circuit breaker cuts off the circuit. The old DC fast circuit breaker has a lot of maintenance work for this part, while the QDS8 fast circuit breaker has a very fast inherent action speed (about 2~3ms). It adopts a magnetic blowing structure and a narrow slit booster arc extinguishing system design to make its rated short-circuit breaking and closing capacity reach 30kA, the electrical life is> 1000 times, which greatly reduces the damage to the contact when the circuit is cut off, which is very prominent in actual use.

2. DC microcomputer integrated protection device

adopt the DC microcomputer integrated protection device? We know that the protection principle of DC fast circuit breaker is that when the fault current is greater than the setting current value of the DC fast circuit breaker, it relies on the "direct over-current instantaneous release" protection action to cut off the fault current. However, in the following cases, only relying on the protection of fast circuit breakers cannot meet the actual use requirements.

1) When the vehicle has a short-circuit fault at the far end of the power supply line, the short-circuit current cannot drive the "direct overcurrent instantaneous release" of the DC fast circuit breaker for protection due to the long line and large loop resistance;

2) The setting value of the "direct overcurrent instantaneous release" protection action of the DC fast circuit breaker of the vehicle is a "single point" instantaneous action, which is very difficult to selectively cooperate with the feeder protection of the superior power supply station, often resulting in leapfrog tripping, and sometimes even "top tripping" the 10kV circuit breaker of the power supply station ".

The ST700 DC microcomputer integrated protection device selected for this transformation can realize the following protection control and measurement functions by sampling the signal of the shunt installed on the main circuit and high-speed sampling of the current (voltage) signal of the power supply circuit through the high-voltage isolation transmitter.

a) The over-current quick-break protection is used to cut off the short-circuit current before the extremely large short-circuit fault current reaches the peak current;

B) Over-current delay protection is used for over-current delay protection of overload faults of lines and equipment;

c) Rising rate protection

rise rate protection is to use the current rise rate (di/dt) and current increment (△I) as the criterion to cut off the short-circuit current in the early stage of short-circuit fault in the protected system, so as to protect the safe operation of the whole power supply system and the train more effectively. The rise rate protection is divided into the near-end short-circuit current rise rate protection and the far-end short-circuit current rise rate protection;

d) Low/overvoltage protection realizes the protection and alarm of voltage drop or overvoltage of line network power supply;

e) Fault recording function

f) Event recording function

g) Electrical parameter measurement and energy metering function

As mentioned above, when the vehicle has a remote short-circuit fault, if a DC microcomputer comprehensive protection device is configured, the "remote short-circuit current rise rate protection" will play a role. The fast circuit breaker realizes the protection action by the absolute value of the current crossing the setting threshold, while the microcomputer protection device judges by the rise rate (di/dt) of the current mutation, so it can accurately judge the remote short-circuit fault; the selective protection of the upper and lower levels is realized through the use of "over-current delay protection" in conjunction with the DC microcomputer integrated protection device of the upper power supply station, which is very obvious after the upgrading and transformation of the power supply station of the power supply plant, basically eliminating the phenomenon of leapfrog tripping.

In addition, through the event recording function and electric energy metering function of the microcomputer protection device, it can also be used as a reference for the operation specification of locomotive drivers and the statistical assessment of vehicle electric energy consumption, so as to minimize the illegal operation of drivers.

3. DC electromagnetic contactor

WLCZ1 series DC electromagnetic contactor is used in this transformation scheme, with a rated working voltage of DC1800V and a rated current of 600A.

The basic working principle of this product is to use electromagnetic coil to control the on-off and off of the moving contact and the static contact. According to the principle of rolling contact, a spring is installed on the moving contact part in the contact unit, and there is a rolling effect when closing, which removes the oxide layer on the contact surface and reduces the contact resistance. Rolling contact makes the lower part of the contact conductive, while the upper part of the contact plays an arc striking role, thus improving the arc extinguishing capability; the arc extinguishing chamber is composed of a number of ionization grids, two arc blowing coils ensure that the arc moves quickly to the arc extinguishing chamber, and the arc is divided into a series of short arcs by the ionization grids, so that the arc can be accelerated and cooled, so as to achieve the purpose of rapid arc extinguishing. Products in the use of the process fully reflects his advantages:

a) The product is electrically maintained, the control system is simple, and the environmental impact is small;

B) The product has small volume, large breaking current and small contact maintenance workload;

c) The product structure is simple and easy to maintain.

3. closing remarks

the above vehicle transformation scheme, through the actual operation test, the effect is very obvious. On the one hand, from the perspective of production, the operation reliability of electric locomotives and higher-level power supply equipment has been greatly improved, ensuring safe production and improving production efficiency; on the other hand, from the perspective of assets, a small amount of transformation capital investment, Let the old equipment that has been used for many years get the same use effect as new equipment, greatly save equipment investment funds, and also reduce equipment maintenance costs. There are still many such old electric locomotives in China, and the popularization and application of this technical scheme can save a lot of investment and create considerable income for enterprises.