The drop has been reported to be to 48.89Hz.
Another fact that made the response difficult was that there was a high amount of renewables (strong wind) and relatively little thermal plant generating at the time with little inertia in the mix, so the imbalance from the production side needed to come from starting up generation from scratch. Pumped storage was turned on almost immediately followed by the open cycle gas turbines.
This is a known issue with greater reliance on renewables, and there is a contract out at the moment for fast response battery provision.
One of the issues of switching from thermal combustion energy to renewable energy is the national Grid has lost much of its "inertia" The heavy spinning mass of large steam driven alternators provided a lot of inertia to the Grid meaning voltage and frequency transients caused by faults were more easily absorbed. Solar, wind nor the dc interconnectors to Europe give much if any inertia to the Grid.
All signalling centres since at least the mid-1960s have had some form of diesel generator backup. More modern centres also have UPS backup. However, in lots of cases, but not all, this does not extend to the lineside supplies that are usually area specific, so if one gets a total outage a relatively small area is affected (on average not more than 5-6 miles). As it happens older mechanical installations can be more resilient that modern systems because everything is obviously mechanically operated, or if electrical, uses primary or secondary cells
Track circuits will naturally 'reset' themselves after power restoration and only show clear if not occupied by any vehicles. Axle Counters will also reset but the affected section will not show clear again until the first train through the section is correctly counted in and then counted out again. Some axle counter systems are fitted with UPS to overcome some, but not all of those issues.
Signals will go out but will restore when power returns. The aspect displayed will depend on what the track circuits/axle counters are telling the signalling system at the time.
AWS▸ will fail to the warning status regardless of signal aspect. The permanent magnet part of it ensures that.
TPWS▸ will fail until power is restored.
Points sometimes have battery backup systems, but not in all cases.
And just for noting; the diesel generators are always tested on-load every thirteen weeks (well they used to be when I once had maintenance responsibility for them).
The large signalling centres (
IECC▸ ,
ROC▸ &
PSB▸ ) do have diesel generator backup which typically take 10 to 15 seconds to come on load from a mains power failure, they have UPS systems to cover for this time, in the more modern ROC these have dual supplies either one
DNO▸ and one (some even have 2 traction and a DNO) where Traction is not used they will have 2 independent DNO supplies.
The problems arise away from the signalling centres at the remote interlocking / relay rooms etc, these will have 2 supplies either DNO with diesel gen as the second supply, DNO with traction as the second supply, in the case of the Southern they have 2 DNO and lost have a third DNO.
All these power supplies take time to detect the supply failure and operate the change over switchgear, this time can range from 2 to 15 seconds, however the supply may be unstable for a second or so before its detected.
UPS are increasingly used, they are sized however typically for 1 to 2 minuets this is only cover the momentary loss of supply while the mains supply changes over to its back up; the economics of providing a UPS that can cover for an hour becomes unviable (ROC UPS are sized slightly lager than a relay room but will still only typically give 15 to 30 mins)
If it was the Class 700 that caused so many problems then I am sure the
TOC▸ ,
NR» ,
ORR» and
DfT» will be placing pressure on Siemens to solve what the issue was, at least when the Class 800 come into full service on the
ECML▸ they can move independent of the traction power
Click on the map to explore geographics
