CTA power control

[MRChiCity]

Hello, I would like to know what CTA Power Control is? I have heard them come up on various CTA rail Channels, is this who is in charge of cutting power to the third rail? Also with incidents involving CFD, I have noticed that the battalion chief often requests a secondary hold on the power, is this an additional safety measure? Thank you  

[cea1991]

There is an employee who sits at a desk at Rail Control behind all of the train dispatchers that specifically handles the system wide power grid. He/She can remotely remove power to any section of the tracks anywhere on the system. CFD has more authority than the CTA, so when the Batt Chief places the secondary hold, it means that the CTA must wait until CFD gives them the all clear. It is an additional measure for safety purposes of all personnel on the right-of-way. Once CFD releases the secondary hold, the CTA incident commander will contact Power and other various units to restore service. 

[MRChiCity]

I have been fallowing the bridge lifts downtown, I have noticed that they will not raise the Lake and Wells Street bridges until power has been cut to the third rail. Why is that? 

[Busjack]

1 minute ago, MRChiCity said:

I have been fallowing the bridge lifts downtown, I have noticed that they will not raise the Lake and Wells Street bridges until power has been cut to the third rail. Why is that? 

Why risk an accident? At a minimum, a CTA train is not the Blues Mobile.

[MRChiCity]

2 minutes ago, Busjack said:

Why risk an accident? At a minimum, a CTA train is not the Blues Mobile.

Couldn't they just signal the trains to stop? And in the bridge towers they have CTA representatives present and tells the bridge operator when power has been cut.  

[cea1991]

1 hour ago, MRChiCity said:

I have been fallowing the bridge lifts downtown, I have noticed that they will not raise the Lake and Wells Street bridges until power has been cut to the third rail. Why is that? 

To truly answer your question it is one about safety, two about drawing as much power to the bridge so it can lift, and three so that if the third rail on the bridge scrapes against the land based third rail, it wont short out the system due to an overload and the breaker will cut out as the amount of electrical flow is not normal. A fail safe will cut all power in the area. CDOT and CTA definitely communicate heavily with one another. The power is setup in sections and blocks. A train can properly birth into Merch Mart, but the tracks that lie ahead passed a certain marker are cut. Does this help? 

[MRChiCity]

Or if a spark hit one of the masts. 

[richii0909]

On 5/28/2018 at 2:12 PM, cea1991 said:

To truly answer your question it is one about safety, two about drawing as much power to the bridge so it can lift, and three so that if the third rail on the bridge scrapes against the land based third rail, it wont short out the system due to an overload and the breaker will cut out as the amount of electrical flow is not normal. A fail safe will cut all power in the area. CDOT and CTA definitely communicate heavily with one another. The power is setup in sections and blocks. A train can properly birth into Merch Mart, but the tracks that lie ahead passed a certain marker are cut. Does this help? 

Question is the third rail isolated in some way? I always saw the 3rd rail as continuous aka bonded line rail. I do see third rail is fed at various points but does the power travel a certain length and then die off. Just trying to get an idea about how it works.

[Busjack]

7 hours ago, richii0909 said:

I always saw the 3rd rail as continuous aka bonded line rail.

It isn't. There is apparently a certain distance of track affected if they cut out a substation, but obviously it isn't continuous, as is more obvious at switches and grade crossings.

[richii0909]

2 hours ago, Busjack said:

It isn't. There is apparently a certain distance of track affected if they cut out a substation, but obviously it isn't continuous, as is more obvious at switches and grade crossings.

ohhh thats right.. thanks for the info

[busfan2847]

11 hours ago, richii0909 said:

Question is the third rail isolated in some way? I always saw the 3rd rail as continuous aka bonded line rail. I do see third rail is fed at various points but does the power travel a certain length and then die off. Just trying to get an idea about how it works.

The conductor (third) rail is supported on ceramic insulators or insulated brackets, typically at intervals of 10 feet or so. It is not continuous and typically switches from one side of the running track to the other, as well as having gaps at switches and grade crossings. Gaps are not a problem as long as the gap is not longer than the train or the train is moving fast enough to coast through the gap! Some early third rail electric locomotives where equipped with a flywheel to keep the loco moving over gaps.

Higher system voltages (above 1500 v) are not considered safe as it becomes increasingly difficult to isolate the third rail. At the 600V dc used by cta, very high currents have to be used to provide the power to move the trains, which leads to considerable power loss in the system, requiring relatively closely spaced feed points (sub-stations). The optimal distance between sub-stations on the "L" is approximately two miles, dependent on loads (The more trains in a section the closer the spacing). There are currently approximately 50 substations around the "L" system.

The return current usually flows through one or both running rails, and leakage to ground is not considered serious.

On newer systems, such as the Docklands Light Rail in London, the third rail cross section is much smaller than conventional systems so the resistance of the third rail, and hence its current loss is much lower allowing greater distances between power stations. Another method for reducing current losses is to use a composite conductor rail of a hybrid aluminium/steel design. The aluminium is a better conductor of electricity (lower resistance), and a running face of stainless steel gives better wear.

[Busjack]

8 minutes ago, busfan2847 said:

The conductor (third) rail is supported on ceramic insulators or insulated brackets,

The other thing this reminds me is that there are concrete (pods or whatever they are called) out of which the feeder cables come that are attached to the third rail, again clearly visible.

The question to which I don't have the answer is how fine the level of control is at the control center, but clearly fine enough to break the circuit somewhere between Tower 18 and the Wells St. Bridge.

[Chicago Bill]

On 5/28/2018 at 12:31 PM, MRChiCity said:

I have been fallowing the bridge lifts downtown, I have noticed that they will not raise the Lake and Wells Street bridges until power has been cut to the third rail. Why is that? 

We don’t remove 600-volt traction power.  That is left on.

When we get a call for a bridge-lift from the Bridge Tender, we follow a list of procedures so the we can provide alternate service if the bridge goes up and we cant get the center locks back in once it goes down.

Once all trains are where we want them to be and Rail Supervisors and Signal Maintainers are in place, for restoration of service purposes, we transfer power (via the Towerman in Tower 18) to the bridge tender so that he can raise the bridge.  It is a safety feature so that the bridge cannot be raised without approval from the CTA.  The Towerman has a switch on the Interlocking Panel that needs to be thrown in order to raise the bridge.  Once the center locks are in place we get notification from the Bridge Tender and we take back power from the Bridge Tender.

A little known fact is that all of the river bridges in the downtown area were once powered by CTA Substations.  Now only the Lake and Wells Street bridges are and eventually they will be transferred to ComEd power.

 

[MRChiCity]

1 hour ago, Chicago Bill said:

We don’t remove 600-volt traction power.  That is left on.

When we get a call for a bridge-lift from the Bridge Tender, we follow a list of procedures so the we can provide alternate service if the bridge goes up and we cant get the center locks back in once it goes down.

Once all trains are where we want them to be and Rail Supervisors and Signal Maintainers are in place, for restoration of service purposes, we transfer power (via the Towerman in Tower 18) to the bridge tender so that he can raise the bridge.  It is a safety feature so that the bridge cannot be raised without approval from the CTA.  The Towerman has a switch on the Interlocking Panel that needs to be thrown in order to raise the bridge.  Once the center locks are in place we get notification from the Bridge Tender and we take back power from the Bridge Tender.

A little known fact is that all of the river bridges in the downtown area were once powered by CTA Substations.  Now only the Lake and Wells Street bridges are and eventually they will be transferred to ComEd power.

 

Cool, I have seen many southbound L trains waiting at Merchandise Mart during a lift. IIRC CTA maintainers are often in the bridge towers during the lift.