500kv Oil Immersed Power Transmission/Autotransformers

Power transformers
Special transformers
Railway
A leader in railway systems
 
Our compact and low-weight transformers fully comply with the customer's specifications. The products are developed together with the clients, ensuring that the requirements of a special pre-qualification process, railway profile requirements and the extreme overload requirements according to EN50239 are always met.
The high quality of our reliable products provides an outstanding capacity to withstand short circuits, which are common in electric railways. Special type tests and quality control ensure safe operation, while Rockwell's product support and service network guarantee free-and -easy use of the product. Special insulating liquids, midel can be used for improved environmental safety and reduced fire risk. the railway transformers are also protected against vandalism.
Railway systems and equipment used in the world are often bound by local national requirements and building practices. therefore, the components must be specially designed and type-tested for each railway for an optimal solution. Rockwell offers its expertise and experience for the railroad builders worldwide for finding the best solutions with rockwell equipment.

Catenary autotransformers
Application 

The electric energy for railways is supplied in high voltage to catenary feeder substations, where the voltage is reduced to a suitable level and fed to the railway catenary conductors to be used by locomotives and trains.
 
Catenary autotransformers are used in modern high-power railway catenary systems fed with two phase with a 180º phase shift, with the mid-point connected to the earth. they are applied to all new high-speed train systems.
 
Purpose
In railways, the electric current is taken from the catenary conductor to the locomotive, where the energy is used by electric motors and fed to the earth connected rails, which are part of the return circuit. In a two-phase fed catenary system, the rail and the earthed return conductor are connected to the mid point of the catenary autotransformer.
 
One pole of the autotransformer is connected to the catenary phase, and the other pole to the negative phase conductor. with this connection, the power is fed to the locomotive with double voltage compared to the voltage of the locomotive itself.
 
This means that the phase currents are reduced to half and the feeder losses to the fourth part compared to the single-phase feeder. The task of the autotransformers along the catenary line is to balance the voltages between the catenary and the earth, and the negative phase conductor and the earth, and then distribute the return current evenly between the two phases.
 
The advantages that are obtained with this connection compared with single-phase feeding and booster transformers are among the following, depending on the objectives:
-lower losses due to higher voltage
-longer distance between catenary feeder substations
-better collection of returning stray currents
-reduced interference for communications

Description

Catenary autotransformers are basically single-phase auto-connected transformers. the primary winding is connected between the two phases and the secondary winding between the catenary phase and the earthed return conductor. The secondary voltage is the catenary voltage against earth, and the primary voltage is two times that.
The requirements for transformers used in electric railways are demanding and special. The impedances of autotransformers are very low; the transformers must tolerate quite high temporary overloading and be resistant to a great number of short circuits.
 
Frequencies in AC-fed electric railways are 16.67Hz,25Hz,50Hz or 60Hz, and the power ratings are 4-15MVA.
 
An Rockwell specialty in catenary autotransformers is the kiosk mounting with an integrated oil sump. The transformer tanks are either hermetically sealed, corrugated and flexible, or vacuum resistant types with detachable radiators and oil conservators.


Booster transformers
Application

Booster transformers are used in electric railway AC catenary feeders to collect the return current from the rails and the earth to the return conductor.

Purpose

In railways, the electric current is taken from the catenary conductor to the locomotive, where the energy is used by electric motors, and fed to the earth connected rails, which are part of the return circuit. From the rails, however, the return current may deviate around to unintended or harmful places like metallic pipelines, bridges, communication cables, etc. the stray current bring about interference in communication systems and other electronic devices due to passing trains. Booster transformers are used to eliminate the stray currents and the disturbances, obliging the return current to flow to return conductor. the use of booster transformers is growing due to new EMC regulations and the increasing amount of sensitive electronic appliances. booster transformers are often used to improve old railway feeder systems.

Description

Booster transformers are single-phase transformers with the ratio 1:1. They have low impedance values, but despite that, they must tolerate the stresses of short-circuit currents. Primary voltages are typically 15Kv or 25Kv, which are the usual nominal AC voltages of catenary feeders in railways around the whole world. The nominal current is usually between 200A and 800A. frequencies in electric railways are 16,67 Hz,25Hz ,50Hz or 60 Hz, and the power ratings of booster transformers are 100-800Kva.
The transformer tank is hermetically sealed, corrugated and flexible, permitting liquid volume variation despite being totally filled. The booster transformer tank is usually hotdip galvanized for corrosion protection. The liquid immersed booster transformer is designed for outdoor installation. The usual style of installation is pole mounting in the catenary supporting steel poles near the catenary and return conductors. An Rockwell specialty in booster transformers is the kiosk mounting with an integrated oil sump pole and ground mountings are also possible.
 

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