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Master Substation
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Distributed Substations
The master substation is located just south of LINAC sector 30. At the master substation, grid power is stepped down to 12KV before being transmitted and used on the SLAC site. The master substation also contains switching equipment used to monitor and control the incoming grid power. Underground transmission lines carry power from the master substation to each VVS, to each PEP region, and to other distributed substations.
At the ends of the 12KV internal power distribution lines, the power must generally be stepped down again to power the devices in the area. The distributed transformers used to do this are located at distributed substations.
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Individual power supplies are used to power magnets, RF stations, and other equipment on the SLAC site. Specific information on power supply systems for different types of magnets is beyond the scope of this discussion of utilities systems, and can be found in the (presently under development) Beam Transport section of this training manual.
Each VVS steps down the 12KV power from the master substation to the 600V used by the modulators. Each VVS is located in an even numbered sector, and provides power to the modulators in both its own sector and the previous sector. The output voltage of most VVSs can be ramped up and down. Thus, when the VVS is turned on, the output voltage can be ramped up gradually, causing less of a shock to the VVS’s internal electronics, and to the modulators. The output voltage of the VVS is controlled by varying a second, lower voltage called the reference voltage. The reference voltage is moved from 90 to 120V, in order to move the VVS output voltage from 450V to 600V. Currently VV11 in sector 22 is the only VVS which does not have a variable output voltage. It is being tested to see if any unforeseen difficulties arise when a transformer with stable output voltage is used. It is still referred to as “VV11” in spite of its non-variable output voltage.
A power glitch can occur due to either on-site power distribution
problems, or off-site problems with the power grid. A power glitch is a
brief interruption of the power being provided to a large number of
electrical devices on site. All electrical devices on site can be
affected by some severe power glitches, while other power glitches can
affect only a few devices. Generally many devices, including water
pumps, air compressors, and power supplies trip off and must be reset
following a power glitch. Power glitches can also cause disruption of
computer network function. Micros often must be IPLed and/or power
cycled, and sometimes network experts must be called to reboot the ALPHA
servers, which run the control system.
When recovering from a power dip, the
operations staff must prioritize recovery tasks, and recover systems in
a logical order. Immediately following a power dip, an electrician
should diagnose the cause of the power dip, and ensure that power has
been restored to all necessary buildings. Maintenance mechanics should
also be contacted immediately following a power dip. They should first
recover the site air compressors. Quick recovery of site air compressors
will prevent the loss of the CID search complete status, and will allow
actuation of vacuum valves and cryogenic system valves. When the site
air compressor is recovered, the maintenance mechanic should begin to
recover water pumps that have tripped. Cryotechnicians should be
automatically notified of any cryogenic system failure, including those
failures that immediately follow a power dip. However, operators should
verify that cryotechs are aware of the power dip, and are responding.
Meanwhile, operators should assess the status of the control system and,
if necessary, contact appropriate experts to help recover the control
system. When the control system has been recovered, operators can begin
to recover failed CAMAC micros and crates, search any areas that have
lost PPS search secured status, clear obstructions (vacuum valves, beam
stoppers, and profile monitors) from the beam lines, and recover RF and
magnet systems. System recovery is prioritized starting with CID
systems, and progressing downstream, so that beams can be turned on in
the injector area and can be brought progressively farther downstream as
equipment is recovered.
WAPA (Western Area Power Administration) acts as an electrical service
coordinator, buying power for SLAC. WAPA communicates directly with the
California ISO (Independent System Operator). In the event that WAPA is
unable to buy sufficient power to meet SLAC’s electrical demand at a
previously agreed upon price, WAPA will contact SLAC to initiate a brown
out. WAPA specifies the time and duration of the brown out, as well as
the site power level that we must stay below during the brown out.
Generally notification of the brown out comes the morning of the brown
out. The SLAC contract with WAPA allows WAPA to request an unlimited
number of brown outs in the months of July and August, and a limited
number of brown outs during the rest of the year. When WAPA requests a
brown out, SLAC has the option of “buying out” of the brown out by
purchasing power on the open market at higher than normal prices during
the specified brown out period. The choice of curtailing power use or
buying power at a higher price is made by the Accelerator Plans Office
and the Accelerator Operations Group head.
In addition to WAPA brown outs, SLAC
is now participating in a separate brown out program with the California
Power Authority (CPA). SLAC receives reduced electrical rates in
exchange for participating in a voluntary curtailment program. Each
month SLAC specifies an amount of power that can be curtailed. In the
event of a CPA brown out, CPA will notify SLAC at 4:00 pm on the day
before the brown out. SLAC may not buy out of these brown outs. The site
power level that we must not exceed is calculated by averaging SLAC’s
peak demand for the last ten days with the highest and lowest demand
days thrown out, and then subtracting from that average the previously
specified amount of power curtailment for that month.
A revision of the MCC brownout
procedure is underway at this time.
The site power meter is located on the west wall of the control room and displays the total power being consumed on site at this time in Megawatts.
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IR2 Chilled Water
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Refrigerated Baffle Chilled Water
The IR2 “Icewagon” chiller is used to cool the Q1 and B1 permanent magnets located very near the IP, as well as several components of the BaBar detector, including the Silicone Vertex Detector. Because the pin diodes used to protect the vertex detector against radiation damage are also highly sensitive to temperature changes, the earliest observed symptom of an IR2 chiller failure is generally a beam independent gradual rise in the radiation level readback from all of the vertex detector pin diodes. Temperature stability for IR magnets is critical to maintaining consistent magnetic fields at the IP, and thus maintaining high luminosity beam optics. Magnet temperature readback for the IR2 cooled magnets can be found trough the following SCP path: INDEX g ANALOG INDEX g PEP RING ANALOG g TEMPS g BEAM LINE NEAR IR g IR2 MAGNET TEMPS. If the IR2 chiller fails, the temperatures of these magnets will begin to rise, however temperature equilibrium will not be reached for several hours. Similarly, when cooling is restored, it may take several hours for the magnet temperatures to stabilize at their normal running temperatures.
There are interlocks intended to prevent beam operation in the event of an IR2 chiller failure. Each of the magnet temperatures that can be found through the SCP path above can trigger a beam abort through the SDS action system if it exceeds the database trip point. If water flow in the IR2 chiller system is interrupted, flow switches trip and trigger the beam abort system through the PR02 Chilled LCW BATS chanel. Also, the QD1R and QD1L TRIM magnets trip off when chiller flow is interrupted.The refrigerated baffle (see vacuum system description) is cooled with a chiller system. In order to achieve typical temperatures of -20 F without freezing, the chiller cools a brine solution. The chillers for the refrigerated baffle are located in the klystron gallery at the end of sector 30. There are two chiller units, but only one is used at a time. In the event of a chiller failure, HVAC techs can switch to the backup chiller. This chiller system has historically run quite reliably, only occasionally needing to be reset after power dips. Analog read back for the refrigerated baffle temperatures can be found through the following SCP path: INDEX g ANALOG INDEX g LINAC ANALOG STATUS g ACC MISC. The analog channels ASTS LI30 DPS_TEM1 and DPS_TEM2 give read back of temperatures at the two ends of the refrigerated baffle.
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There are three cooling towers for LINAC and damping ring water systems. One cooling tower complex near MCC provides cooling water for PEP, and for some research yard water systems. Another cooling tower (404) has recently been built in the research yard area to provide cooling for SPEAR and the Central Helium Facility.
| Tower # | Location | Description |
|---|---|---|
| 1200 | Near SDR | Cools water for DRxx, LI00, LI01, and LI02. (note: damping rings also have a separate low pressure water system for cooling power supplies) |
| 1201 | Sector 9 | Cools water for LI03-LI15 |
| 1202 | Sector 22 | Cools water for LI16-LI30 |
| 1701 | Near MCC | Cools water for research yard systems. |
| 1703 | Near MCC | 1703 tower is an add-on to 1701 tower, and is used to cool PEP water. |
| 1801 | Near MCC | 1801 pumps provide research yard LCW for BSY, ESA, ESB, ESC, FFTB, SPEAR, and SLC arcs. It uses a heat exchange mechanism with the 1701 cooling tower. |
| 404 | Research Yard | CT404 is a basin-less cooling tower used to provide cooling water to SPEAR and the Central Helium Facility (Bldg. 127). It is also slated to be used for LCLS cooling. |
In the LINAC, there are three separate LCW systems in addition to several independent rad-water systems. Rad-water systems are closed water systems providing water to cool devices designed to absorb a lot of beam power, and therefore are expected to become radioactive. Special radiological procedures are followed when doing maintenance work on rad-water systems to protect workers and prevent the spread of radioactive contamination.
Non-radioactive LINAC Water Systems:
| System Name | System Description |
|---|---|
| Klystron Water | 1 pump every three sectors: Sectors with pumps = 3N-1, where N is an integer. |
| Devices Cooled: klystron focus magnets, klystron body, subbooster, QUAD magnet coils, magnet power supplies, I&C alcove equipment, and other upstairs devices. | |
| Temperature Stability: not very important. | |
| Note: Klystron water in most sectors is not classified as rad-water, but klystron water in sectors 5 and 29 is rad-water. | |
| Waveguide Water | 1 pump per sector. |
| Devices Cooled: Main Drive Line, Phase Reference Line, Sub-drive line, rectangular waveguides. | |
| Temperature Stability: important. | |
| Note: heat load for this system is low compared to other systems. | |
| Accelerator Water | 1 pump per sector. |
| Devices Cooled: Accelerator Structure (pipes along sides of disc loaded waveguide), SLED cavities (after water returns from accelerator structure) | |
| Temperature Stability: very important. | |
| Note: in order to help maintain a constant temperature, there are heaters hooked up in series with the heat exchanger for this system. |
Rad-water Systems:
| System Name | System Description |
|---|---|
| BAS-II Water | Cools: BAS-II dump, some positron system items. |
| Pump Location: blockhouse in sector 20 | |
| Collimator Water | Cools: Sector 30 collimators. |
| Pump Location: cement enclosure near radioactive materials storage area (between MCC and sector 30). | |
| Slit 10-30 Water | Cools: 10-30 Slits (A-line momentum collimator/ beam stopper). |
| Pump Location: cement enclosure by MCC lower parking lot. | |
| Beam Dump East Water | Cools : Beam dump at end of A-line. |
| Pump Location: Inside BDE PPS area. | |
| A Beam Dump Water | NO LONGER IN USE |
| Pump Location: by AN4 entrance to ESA |
Water flows from the cooled device toward the heat exchanger and comes to regulator 1. Regulator 1 monitors the temperature of the water going back out to the cooled device, and adjusts the amount of water going through the heat exchanger in order to regulate the temperature of the cooling water. The regulator sends some of the water through the heat exchanger, and allows the rest to bypass the heat exchanger. The water is then recombined after the heat exchanger, and pumped back out to the cooled device. On the opposite side of the heat exchanger, regulator 2 measures the temperature of the water going to the heat exchanger, and adjusts the amount of water going through the cooling tower vs. the amount of water bypassing the cooling tower, in order to maintain a constant temperature at the heat exchanger.
Demineralizers remove dissolved minerals from water by blowing the water in to a tank of ion exchange resin, which removes the ions from the water. The demineralizers reduce the electrical conductivity of the water.
The still cleans the water by evaporating the water and then recondensing it.
Deaerators remove dissolved oxygen from the water.
Sand Filters are strainers that remove particulates from the water.
Containment sumps are ditches around each of the pump
pads, which will contain the water if a leak occurs anywhere on the pump
pad.
When the high power electron beam passes through water, it breaks the water molecules apart into hydrogen and oxygen gas. The recombiner turns the hydrogen and oxygen back into water. If the Hydrogen recombiner were to stop working, the build up of hydrogen gas in the water pipes could create an explosion hazard. For this reason, the hydrogen recombiner is interlocked to the MPS system, and actuates a warning on the MCC audible warning panel. Further information about this warning and the proper response can be found in the warning and alarm response procedures. There are hydrogen recombiner systems for the sector 30 collimator water system, the Slit 10-30 water system, and the beam dump east water system.
| System Name | System Description |
|---|---|
| RF water | Cools PEP RF cavities. |
| HCS water | High conductivity water system cools RF loads. |
| KLYS water | Cools klystron focus magnet and collector. |
| MAG water | Cools magnets (also known as “aluminum” system because pipes are aluminum) |
| VAC water | Cools vacuum chambers (also known as “copper” system because pipes are copper) |
The site compressed air system has three air compressors located in building
23. There are two 200 horsepower compressors and one 60 horsepower
compressor. In order to maintain adequate site air pressure, any two out of
those three compressors must be running. The air pressure at building 23 is
maintained at 110 to 128 psi. However, the air pressure drops as the
compressed air is distributed around the SLAC site, so that the actual air
pressure at a device actuated by compressed air is always lower than the
pressure maintained at building 23.
Compressed air is used to actuate
many systems critical to beam operation. The concrete shielding blocks at
CID and the positron vault are moved with compressed air, and may open and
cause a PPS fault if the site air pressure is too low. Many vacuum valves
are site air actuated, and will fall in and not be able to be pulled out
without adequate site air pressure. Cryogenic systems depend on site air to
actuate valves within the cryogenic system. Site air is also used to actuate
the water system valves which regulate the flow of water through heat
exchangers and cooling towers.
There are several diagnostics that
operators can use to monitor the site air system. There is SCP analog read
back of the air pressure in LI00 available through the CID analog panel on
the “CID MISC” display. There are also air compressor alarms and faults
reported through the DCS (Distributed Control System), and used primarily by
instrument techs. In the event that the control system is down and operators
need to know the status of the site compressed air system, there is also an
analog pressure gauge located outside the northwest corner of building 5. It
shows the compressed air pressure at the location of that gauge, and
normally runs at about 115psi. An image showing the location of this gauge
is shown below.
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SLAC cryogenic systems do not provide readback to any SCP, EPICS, or hardware control panels in MCC. There are local controls operated by the on duty cryotech at the Central Helium Facility, at IR 2 for BaBar systems, and at CID for P-Gun systems. There is an automatic paging system to alert offsite cryogenic system experts of possible problems, and web-based diagnostics to allow remote troubleshooting. These diagnostics are designed to be used by cryotechnicians and cryotech supervisors who need to monitor and investigate trouble with cryogenic systems from off site, but can also be useful for MCC operators. Links to these displays can be found through the EFD (Experimental Facilities Department) web page, or here:
BaBar Cryogenic Systems
Research Yard Refrigerator Facility(Note: These links may not work during periods when the cryogenic systems are not operating.)
Although cryogenic systems are listed in this manual as “utilities” because of their function providing cooling to several accelerator and detector components, it is important to note that many components of the cryogenic systems are dependent on other site utilities including electrical systems, compressed air systems, and cooling water systems.The following schematic diagram shows the general layout of the SLAC cryogenic system.
