Success Story : Protection Scheme Audit of 220kV GIS

One of the primary themes of our blogs has been on emphasizing the need for regular testing and maintenance of electrical assets. Some of these discussions are hyperlinked here for quick reference: a) testing and maintenance of electrical equipment at a steel manufacturing plant, b) earthing and lightning protection system audit and c) health assessment of transmission line towers.  Regular testing and maintenance can result in maximizing the utilization of existing assets, reducing asset down-time, and saving on potential financial losses for investors.

In this blog post, we will share yet another success story involving our service vertical – ISOSCELES (ISSPL). In this instance, ISSPL was awarded a contract by a leading company in the IT sector to audit the protection system of their 220 kV GIS substation.

Background of the case

In this instance, ISSPL – a leading provider of services for operation and maintenance of electrical assets – received the purchase order for audit of the protection system of 2 numbers of control and relay panels (CRP) in the 220 kV substation. The customer approached ISSPL to complete this task as part of their regular maintenance testing, conducted annually. ISSPL team was immediately deputed to the site for complete testing of transformer protection panel.

Description of Audit

On commencing the audit, ISOSCELES service experts observed that the REF (restricted earth fault) scheme was improper. Service experts observed that the bushing CT (current transformer) is not associated with REF protection. As the REF was working on combination of NCT (neutral CT) and HV bay CT, the REF relay would trip further causing a cable fault.

Furthermore, second HV bushing CT of transformer is connected on tertiary coil of the relay. ISOSCELES experts diagnosed that the relay was not configured as per the protection scheme. Both REF and differential protection was enabled in the same relay and there was no redundancy for relay.

Additionally, REF was not implemented for LV side. It was also concluded that the supplied relays were not suitable for the protection scheme. Based on these observations, our service experts recommended that:

  1. The bushing CT connection be removed from the differential relay
  2. LV REF scheme be implemented and
  3. Use standalone REF relay as redundancy relay
Photo Courtesy – Elec -Engg Portal

Challenges faced

In order to conduct this detailed audit of the protection system, ISOSCELES service experts used 3 phase relay testing kit . ISOSCELES team recommended such kit as it would quickly resolve the issues faced by the customer, thereby minimizing down time. While conducting this audit, ISOSCELES service experts faced many challenges:

  • CRP panel was not configured as per the standard scheme. Furthermore, relay did not have the functionality which enabled communication with a laptop. This meant that the service experts had to request for the manual and the existing configuration file from the customer. On receipt of the same, service experts ensured proper configuration of the relay as well as the wiring.
  • While ISOSCELES service engineers are experts in the field of testing and maintenance of critical electrical assets, the experts deputed on site did not have prior practical experience of working with the make and model of relays installed on site. This challenge was met head on and the panel was configured in the appropriate manner
  • Based on the analysis of the service experts, we recommended that the customer purchase a separate LV REF relay.


The following are some key takeaways from our experience on site:

  1. A major learning from this case is the criticality of ensuring that the relay firmware should match with the protection schematic. However, this problem was identified on account of the testing and maintenance audit performed by the ISSPL service experts.
  2. Given the criticality of relays at an electrical substation, it is essential that the wiring and protection scheme of the CRP should be examined regularly on annual basis. Such regular testing will reduce probability of outages in the substation, an event that can have critical implications for industrial customers.

While it is assumed that audit of protection systems of a substation is an activity that is restricted to electrical utilities, industries also need to pay attention to regular testing and audit. Given the increasing ubiquity of SEZs and similar manufacturing zones, industries often set up manufacturing localities which require an electrical network on top of the grid network provided by the local electricity utility. Any outage occurring out of a fault in the electrical system can result in down time and loss of revenue.

To know more about ISSPL’s protection system audit capabilities, please visit or write to us at

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