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Upgrade to 8 x 9’s Availability!
Have You Audited Your Sites For Single Cord Loads Content? If Not,
Then You Have Hidden Risks Waiting for a UPS Failure To Surface!
Implement TwinSource Rack Mounted Static Transfer Switches (RMSTS)

What does 8 x 9’s availability mean? TwinSource RMSTS installed base of systems worldwide have as of October 1, 2007 clocked in at over 40 million hours of actual critical load operation hours without a load incident. This impressive operational data yields over 8 x 9’s availability. To put this into a more tangible measure consider that a Tier IV data center with 4 x 9’s availability yields an expected average outage per year of 52.56 minutes whereas a TwinSource protected rack yields an expected outage per year of only 0.031 seconds which reflects an improvement in reliability of 100,000: 1. These are not calculated or projected numbers. The 40 million hours is an actual measurement of “unit hours” across all sites without any load incidents. The best replacment product for your failing APC transfer switch.

TwinSource RMSTSs Installation in Racks

Rack mount static transfer switch

How does it do it? The system does this via an array of built-in redundancies, very conservative component ratings, as well as operator error prevention techniques. Contact TwinSource for details on their rack mount static transfer switch if you want to replace the APC transfer switch. Another impressive data point: No TwinSource systems have ever dropped a load because of an operator error. We do this with our optional operator error prevention interlocks. With these options you can’t bypass these units to the wrong side of the SCRs, cause a source to source short, or bypass to a source that’s outside your power quality specifications and drop the load. This is because the rack mount STS will alarm you to not bypass before you get there.

How fast do they transfer and can they do this at 180 degrees? These are super fast switches. They transfer the load in less than ¼ cycle even if the sources are 180 degrees out of phase. Here is an actual trace with the sources out of phase by 180 degrees and Source 1 was failed to cause a transfer:

Conditions: Low power factor inductive load.
70% load, 180 degrees out of phase
S1 turned off to cause transfer to S2
Total sense and transfer time: 4.1 ms

How do you access them for maintenance actions? This is easy. The unit comes with a built-in outer bypass isolation module and a plug-in electronic module that plugs into the bypass module but can be withdrawn and replaced without bothering the load. There is no opportunity to make field repair errors because each time you replace the entire electronics. This also reduces the MTTR to less than 5 minutes. In less than 5 minutes of an alarm, you’re back to normal operation. No troubleshooting or repairs are required. No waiting for someone to call
you back or arrive is required. By the time you would get a call back on a trouble call, you’re back to normal. See the electronic module partly pulled out in the photo below:

 Twinsource rack mount static switch with bypass

How do I implement them into my 2N system? This too is easy and a 2N system is not required as the preferred source to the RMSTS (rack mount static transfer switch) can be a UPS and the alternate can be any other
source including utility. The predominant use of these systems is no doubt to protect the single corded loads. As much as everyone tries to avoid single corded loads, many exist in every data center and this becomes your weak link that can cause major disruptions. If there has never been an accurate audit of your single cord load contents across your sites, you have hidden risks waiting to pop up as soon as you have any power disruptions. Why? Because while your dual cord loads are fed from 2 UPSs and are always protected, the single cord ones will drop as soon as one of the UPSs fails or if you have to take a device in your distribution out of service; a device that feeds some of the single cord loads. Rather than wait until a UPS fails to discover how bad this can be and call us, be proactive and afford your single cord loads the same level of reliability as your dual cords. A good design aims for uniform
reliability of devices across the floor and the infrastructure. The diagram below shows the simplest application of RMSTSs to protect only the single cord loads:

Typical 2N single line diagram showing the 2x 2N UPSs, distribution devices & a typical rack with onlysingle loads. Dual cords are simply fed directly from the RPPs.

The diagram below shows one typical way the TwinSource RMSTS can be applied to all single corded loads as well as some of the super critical dual corded “must always have on no matter what loads”, if such exist. Alternatively you could double up on your single corded loads but this requires more capital, more rack space, and generates more heat.

Typical 2N single line diagram showing the 2x 2N UPSs, distribution devices & a typical rack with both single and only the super critical dual cord loads. Other less critical dual cords are fed directly from the RPPs. Note that in this case any PDU or RPP can be isolated for service without losing the 2N capability which would otherwise be lost if any device is isolated for maintenance actions.

In the above figure it is clear that the “super critical dual & single cords” can also be provided with ultimate protection using a third UPS.

Feed the first “Switch 1” by the same UPSs A & B above and feed its output to Switch 2 as well as to Cord 1 in the rack and the second source of Switch 2 is fed from a UPS C and its output is connected to Cord 2 in the rack. Connect the dual cords between the cords and the single cords on Cord 2 so they too can benefit from 3 sources. In a 3 megawatt data center for example you can feed all regular dual and single cords from the large UPSs A and B (no switches for dual and only one switch for single) and the most super critical dual & single cords also from a 3rd UPS that is only rated at say 200KVA (= the total KVA of all super critical single cords + all super critical duel cord loads). This provides an unmatched level of availability with 3 source capability. This configuration is shown below:

Typical 2N single line diagram showing the 2x 2N UPSs, distribution devices
& a typical rack with only the super critical dual cord loads fed from a 3rd UPS. Other less critical dual cords are
fed directly from the RPPs from only 2 UPSs.

Questions? If you’d like to implement RMSTS solutions to increase your availability numbers and be rid
of concerns over your single cord load loss impact please contact us.