Kestrel substation retrofits
New protection relays at 14 live substations on a regional network.
14 substations,
no unplanned outage
Size
14 substations, 110 kV
Location
Northern Germany
My role
Protection design and site lead
Team
4 engineers, 2 site crews
Duration
31 months, 2016 to 2019
01
The situation
Kestrel looked after a regional 110 kV network in northern Germany. Fourteen of its substations still ran on mechanical protection relays from the 1970s and 1980s. These are the devices that detect a fault and tell a breaker to open. Spare parts had run out, and only two technicians still knew how to calibrate them.
The substations fed towns, a port and two hospitals, so none could be switched off for more than a few hours. The relays had to be replaced while the stations stayed live. A wrong setting in a new relay does not show on the day. It shows months later, as a blackout nobody expected.
02
What I did
I designed the new protection scheme for each substation and calculated the settings for 212 digital relays. I checked each setting against a model of the network in PowerFactory. Then a second engineer checked it without seeing my numbers. Where our answers differed, we stopped and worked out why before anything was ordered.
On site, we replaced one section at a time while the others carried the load. I wrote a switching plan for every outage and agreed it with the control room a week ahead. I stayed at each substation until its last relay had been tested by feeding in a simulated fault and watching the breaker open.
03
What changed
All 14 substations were upgraded between 2016 and 2019 with no unplanned outage. Every planned outage was handed back on time or early. In the first winter after the work, the new relays cleared three real faults on overhead lines. Each one was cleared in under a tenth of a second, and only the faulty line was switched off.
The double check on settings became a rule in Kestrel’s design office. It added about a day per substation and found nine errors before they reached site. Four of them were mine. I have used the same rule on every battery project since. It is the cheapest insurance I know.
14
Substations upgraded while live
2016 to 2019, 110 kV network
212
Protection relays replaced
Each setting checked by two engineers
0
Unplanned outages during the work
Control room outage records
“She would not leave a station until she had seen every breaker open with her own eyes. Our control room trusted her switching plans completely.”
Annika Dreyer
Head of Network Operations, Kestrel Grid Services