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  Introduction
In today's day and age, heating devices for switch points in areas where the climatic conditions demand it, are a conceivable component of railway equipment. Such equipment contributes to increased safety and smooth operations and, as it decreases the amount of hazardous work involved in cleaning switch points, also saves expenses related to personnel resources.
A Description of the Equipment
The electric heating devices are powered either by contact systems with alternating current (15 kV, 25 kV) through single phase transformers, or, in the case of contact systems with direct current (3 kV, 1,5 kV, 750V), through converters. Power can also be supplied through a distribution grid network. The output of the transformers or converters is a 2 x 230V voltage which can also be adjusted according to the needs of the customer. The frequency is either 50 or 60 Hz. The frequency is always sinusoidal (even when converter is used).
When power is supplied by a contact system, the high voltage input lines are led through a motor-driven disconnecting switch and a fuse. This equipment is installed on a pole. A lightning arrester is also attached.
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| Disconnecting switch, fuse and lightning arrester |
The motor drives for disconnecting switch |
In the case of alternating current, the leads are attached to a cable connected to the primary winding of a transformer. The output connector from the primary lead is connected to the rails with rail circuits through the center of a contact transformer located by the rails or directly to the rails when the nature of the security equipment allows it.
The transformer is usually installed in housing manufactured from special "aluzinc" metal which is known to be highly anti-corrosive. The housing is divided into two sections by a partition. The transformer is housed in one section and a low voltage distribution board is in the other. For safety reasons, the housing is connected to the rails through a circuit breaker.
The low voltage distribution board is connected to the secondary coil of the transformer by a cable leading through the partition of the housing unit. The output lead is grounded by connection to a independent grounding unit.
The transformer may also be installed in an alternative location, for example on a power pole. It is then connected in the same manner as if it were in a housing unit.
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| The housing unit for a transformer |
A high-voltage fuse and transformer |
In the case of direct current, the input is connected by a cable to the input connector on a converter. The output connector from the primary section is connected to the tracks with rail circuits through the center of a contact transformer located by the rails or directly to the tracks where the nature of the security equipment allows it.
The converter is located in housing designed along similar lines as that which is used in the case of transformers. The design of the exit circuit is the same as that of the secondary circuit of the transformer. The grounding of the non-live section is also identical.
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| The housing with the converter (the 3 kV side) |
The housing with the converter (the low-voltage side) |
The converter which is used is of modern construction with IGBT transistors. It is mounted in a steel frame which is designed for easy manipulation. Cooling is forced through a series of fans as it is necessary due to the small dimensions and high level of output. The standard converter which is delivered has an output of 60,90 or 190 kW. Power contactors and security fuses are components of the converter. The primary potential is 3kV DC +/- 33%. The secondary potential is 2 x 230 V +/- 5%, 50 Hz sinusoidal waves. The power for charging the control circuits is 24V obtained from 230V/24V power sources. More detailed information about the converters can be found in the separate documentation.
60 kW converter
If power is obtained from a distributed network, a cable from the distribution transformer station or from the station's main distribution board is connected to a low-voltage distribution board. In this case, the low-voltage distribution board is installed in plastic housing.
Low-voltage distribution boards when using power from a distributed network
The feed lines used for heating individual switch points then lead from the low-voltage distribution boards. Cables for powering the main heating elements are separate and are placed on the tracks at the switch point. The cables for the heating elements for the locks and switch lever handles are placed in the area between the sleepers under the switch lever handles for the switching device. The independently heated area around the operating switch lever handles and locks of the switch point are highly advantageous as opposed to the assembled equipment used in the past.
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| The main heating of the rails |
Heating of the switch lever handles and locks |
The distribution between the distribution board and the terminal cases located trackside for individual switch points is accomplished by means of copper-core cables with a cross-section of 4-10 mm2 dependent on the power input and the distance of the switch point from the distribution board. The housing and the heating elements are connected by a heavy rope protected by a plastic hose.
The casing used for the terminals used to connect the heating elements
The apparatus is equipped with a control system that has a programmable unit which provides automatic regulation of the heating and also includes a remote control. Control is managed based on the air temperature, the rail temperature and based on the presence of precipitation. Heat and precipitation sensors are used for this purpose. The heating of the switch lever handles and locks is managed separately and independently. The on-going monitoring of the heating functions is at a high level. For example, in the event of a malfunction of any of the heating elements, notification is immediately transmitted to selected locations (for example, the railway station office, central dispatching, etc.). Unauthorized entry to the equipment, damage to the sensor and other problems are also monitored and announced.
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| The programmable monitoring units |
Temperature and precipitation sensor |
Connectivity between the location of the remote control and the monitoring system is achieved through a standard RS485 interface. The remote control and monitoring system may be placed anywhere according to the user's wishes. It is also possible to install a PC with a visual program.
During normal operations, the equipment functions completely automatically. A decisive factor for the automatic activation of the heating system is when the pre-specified air temperature, rail temperature and also the presence of precipitation is registered. If necessary, the heating may also be turned on manually in test mode. If the heating is turned on by such a method, it automatically turns off after a pre-specified period of time. This mode serves to control the proper functioning of the equipment, for example, during the summer months or after maintenance work is performed on the switch point.
The use of the equipment can be monitored either indirectly based on recording the number of hours it is in operation or directly, by measuring the use of electric energy.
Safeguards against the hazards of touching the non-live components on the low-voltage side if the isolation has been damaged is provided through current protector switches which function on the basis of monitoring the amount of escaping current. A large advantage of this system is that it does not use expensive, faulty and dated separator transformers located in the area of the rail tracks.
When a contact system is used for obtaining power, the circuits of the heating elements have a standard voltage of 2x230 V, 50 Hz. When power is obtained directly from a distributed network, the circuits of the heating elements have a standard triple-phase voltage of 3x 230/400 V, 50 Hz. The actual voltage may vary as may the frequency (16 2/3 Hz, 60 Hz).
The equipment used for heating the switch points is technically developed, manufactured and delivered with a level of quality which will withstand speeds of up to 300 km/hr.
The method used for attaching the heating elements allows for easy installation on any type of rail. The heating elements are manufactured of rust-resistant steel. They are available in several lengths. The output is generally approximately 300 W per meter but may be even higher. The heating elements are characterized by high quality and a very long service life. If however any malfunction should occur, usually as a result of mechanical damage caused, for example, by packing, the replacement is quick and simple.
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| The heating element for heating the rails |
The heating element for heating the locks and switch lever handles |
Conclusion
The equipment is flexible and may easily be adapted according to the user's requirements. The final solution which is implemented is always based on the project documentation according to the location of the switch points and the required power input. The manufacturer guarantees the delivery of the equipment, including its installation, brings the equipment into operation and provides warranty as well as post-warranty service. Similar equipment in many of its variations has already been installed on hundreds of switch points in several countries.
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