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An issue was encountered during transformer rectifier upgrades on London's Underground. The upgrade in question sought to change over TR units of 1.5 MW rating with those of 2.5 MW rating however the existing 11kV protection relay (GEC CDG11) could not (for logistical reasons) be practicably changed over at the same time as the TR unit. The integral Standard Inverse protection curve offered by the CDG11 relay would normally not be suitable for use with the new 2.5 MW TR unit so a solution to this dilemma had to be sought.

PND proposed a solution to the problem by using a combination of mathematics, knowledge of CDG relays and software modelling to construct a proprietory algorithm enabling the CDG11 Standard Inverse curve to be safely used with the 2.5 MW TR unit. The change over of the protection relays from a CDG11 to an Alstom P122 model could then be deployed at a more feasible time. The method was proposed to the Client and subsequently accepted for use for use across the entire upgrade program.

CTRL Domestic Service power supply system modelling was undertaken on behalf of Network Rail in a bid to understand the impact of the proposed CTRL DS services on the power system. The modelling covered the 750V DC electrified route from Springhead Junction to Ramsgate.

The affected electrification system was primarily comprised of four Grid supply points feeding the 33kV HV distribution system which in turn supplied around twenty DC traction substations.

The electrification system performance was evaluated under both normal and degraded modes of operation. In terms of the HV system, this comprised analysis of both normal and extended feeding conditions and for the DC system, single transformer rectifier outages.

Risks to both the 33kV and 750 DC system were highlighted as part of the modelling exercise. Recommendations were made (and accepted) in order to manage their impact e.g further mesurement and analysis coupled with network reinforcement where neccessary.

The protection studies quoted were carried out by PND's staff to ensure that Network Rail's new power system infrastructure could be safely energised whilst at the same time making provision for the new rolling stock to enter passenger service. Such studies primarily related to the 33kV and 11kV systems as well as the dc traction system.

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