Compensation of Earth Fault Current

Ensto has extensive experience in providing turnkey solutions for compensation of earth fault current to underground cable networks, covering everything from needs assessment to commissioning and maintenance.

Increased Need for Compensation for Earth Fault Current

The requirements of distribution system owners regarding the reliability of electricity supply are getting stricter. As a result of the tightened regulations, underground cabling in distribution networks increases constantly. Cabling in turn significantly raises the earth fault current in the networks and the earth fault current generated by underground cables is approximately 40 times higher compared to overhead lines. This will lead to an increased need for earth fault current compensation.

Ensto has extensive theoretical and practical knowledge and thorough experience in providing earth fault current compensation solutions for the underground cable distribution networks.

Full Service on Turnkey Basis

Our earth fault protection solution detects and isolates high impedance earth faults with world’s best accuracy shortening the duration of outage time. The turnkey services include all from the needs specifications and device deliveries to commissioning and maintenance services, which includes e.g. need assessments, equipment, design, installation, commissioning, protection relay setting changes and testing and primary earth fault tests.

In addition, we take care of the annual maintenance of the equipment. The solutions are always carefully planned based on and configured to meet the customer’s needs.

Our Solutions

Centralized Compensation

Earth fault current compensation has traditionally been handled with a centralized compensation system, where the entire earth fault current of the galvanically connected network is compensated with a single adjustable arc suppression coil. The compensation system is usually placed in its own protective building within the substation area.

In the deliveries of earth fault current compensation equipment, Ensto uses Austrian Trench equipment, which are known worldwide as the best in the field. Trench also manufactures earth fault compensation controllers, ensuring seamless operation of the system.

Centralized Earth Fault Detection EFD

Ensto centralized earth fault detection, EFD, offers many benefits for the customers:

Selective detection and tripping of high-resistance faults.
Reliable and selective detection and tripping of intermittent earth faults.
Reliable and fast determination of the turning point, even in symmetrical networks (e.g., cable networks where the resonance point zero sequence voltage is low).
An intermittent earth fault often triggers the busbar Uo relay, which trips the substation feeder circuit breaker. Selective tripping of the intermittent earth fault significantly reduces outage time.
The EFD device provides early warning of faults in the feeder, allowing for fault location and preparation for repair work before an interruption occurs.
The EFD device can be connected in parallel with the existing protection and can initially be set to alarm-only mode, for example.
With sensitive earth fault impedance indication, the system can be used as a tool for condition monitoring (trend data on earth fault impedance can be sent to remote control systems).
The system monitors the entire network simultaneously (Io measurements from each feeder). The sensitive protection detects changes across all feeders during fault situations (the measurement data is time-synchronized precisely for all feeder measurements).
The analysis of measurement data uses both transient and admittance methods (the transient method for intermittent earth faults and the admittance method for high-resistance faults).
It can be connected to most bus systems and supports all common communication protocols.

Decentralized Compensation

In certain cases, it makes sense to use distributed compensation and place the compensation coil directly in the network as a fixed installation. In a fixed compensation, a specific cable or area can be compensated, which saves the capacity of the centralized compensation system. The compensation coil can be installed, for example, in our smart substation, through which measurements and monitoring for the equipment can be handled simultaneously.

Service and Maintenance

Annual maintenance of the earth fault compensation equipment ensures reliable operation as the equipment ages, which helps to avoid possible problems. It is also possible to update the compensator's software to a newer version during the annual maintenance.

Our maintenance service can be completely customized according to the customer's needs – either as individual maintenance or as a comprehensive service. In a comprehensive maintenance service, we take care of the maintenance history, monitor future maintenance needs and ensure that the work is completed on time.

Checking the function of the parallel resistor with a primary test (can also be determined if a fault recording from the earth fault is available)
Inspection of earth fault protection parameters and controller settings (during relay testing or specially if the cable length of the network has changed substantially)
Checking the operation of a possible star point disconnector
Inspection of the operation of the basic angle control circuit
Checking the limit switches of the arc suppression coil by driving the motor to the upper and lower limits with the ASC disconnected from the network. At the same time, the operation of the ASC motor is checked.

Equipment Shelters

The equipment shelter is a secondary substation-type building designed for compensation equipment and meets customer requirements excellently in terms of usability, ease, appearance, and cost-effectiveness.

The equipment shelter is more spacious than a secondary substation, making it easier to audit and maintain the equipment. The overall design of the shelter can always be defined according to the customer's needs. Available standard size models (foundation external dimensions):

2,4m x 5,8m
2,4m x 4,5m
2,4m x 2,65m

Sustainable Finnish Design

The design of the equipment shelter considers the maximum snow and wind loads prevailing in the north. Comprehensive strength calculations have been made for the structures, also considering the stresses caused by lifting the building. The equipment shelter is delivered to the site ready for use together with the foundation basin.

The foundation is a uniform and flat-bottomed concrete element basin, in which the equipment shelter can be freely placed. The foundation also serves as a fire-safe and durable oil collection basin. The foundation design also focuses on easy installation.

If necessary, the equipment shelters can be equipped with enhanced natural ventilation or blowers. The manufacture of equipment shelters is ISO 9001, ISO 14001, and ISO 45001 certified.