This LinkedIn group was created to provide “cutting edge information about trends, new products and developments” in respect to Static Transfer Switches and critical power applications. The discussions in this group will to help inform and also negate misinformation of issues for differing STS alternatives and options.
Some people know about “Static Transfer Switches” or STS, however there is confusion within the community of users and customers about the functionally of similar products and ultimately what you get for your dollars with an STS.
Let’s begin the discussions with a typical scenario where an end user purchases a transfer switch.
An IT specialist or a manager of a data centre discovers they have a vulnerability issue when they lose power. Perhaps their UPS or battery backup failed or someone turned off the wrong breaker within their power distribution system. Without comprehensive knowledge of the technical specifications, they look on the internet for an affordable transfer switch and purchase it. They test it out by connecting it to a computer, which stays on and so leaves them believing that they are now fully protected. Many months later there is another power outage where some of their equipment fails, causing serious repercussions for the company. The supplier of the transfer switch doesn’t understand why the fault occurred because they do not specialise in transfer switches, they only specialise in the sale of UPS, products and ancillary services.
This is a scenario that we hear about a lot.
When purchasing equipment for critical power protection, too often decisions are made on the price, look and feel of a product. Fiscal frugality can leave you with faulty equipment that ultimately hurts the company’s bottom line and reputation.
So how could a transfer switch let you down? To answer this we need understand technical limitations of some types of equipment:
1. The switch uses relay components. Relay switching components have longer break times, which can vary depending on nature of the loss or sag. Break times are typically 12-35 msec which is equivalant to ½ – 2 cycles. Any break in power larger than 20 msec may cause issues for your critical equipment.
2. The switch is a hybrid type. Some transfer switches marketed as STS may actually use a combination of both solid-state devices (Thyristors / SCRs) to undertake the initial change-over followed up by bridging relays. Transfer speeds are slower than a true Static Transfer Switch as they are limited by the speed of the electromechanical relays. In hybrid types, the solid-state devices are smaller and have almost no over-capacity. The contacts on relay / hybrid switches are prone to welding or blowing open, causing source to source issues as a result and affecting all connected equipment.
3. The switch uses voltage sensing only. Without current monitoring the device will not be able to detect downstream failures such as a short circuits and will transfer the load fault to the other supply, which can result in a loss of both sources.
4. The switch performs synchronous transfers. An asynchronous transfer that does not occurs zero point crossover of the waveform can send inrush current the load and cause issues for the connected equipment.
5. The switch has no source lock out. If the switch uses relay components and does not have a locking feature to remain on one supply, it can continually transfer between the sources until the components break.
6. The switch is not rated for high power environments. Devices that contain no fuses, or have limited capacity circuit breakers, or underrated switching components, are unsafe for high power environments and could cause fires if they are overloaded.
How is possible to end up with an inferior transfer switch, or one that relies on relay-based switching components? Suppliers can market relay based transfer switches as “STS”, where in this contexts the acronym stands for “Source Transfer Switches”, not “Static Transfer Switch”. They can also be called “Automatic Transfer Switch” or ATS. When it comes to terminology be careful and do your research!
A true Static Transfer Switch is often described as a “Solid-State Static Transfer Switch” or ”Solid-State Transfer Switch”, abbreviated as STS or SSTS.
The iSTS products manufactured by Static Power, are true solid-state transfer switches that excel in performance and reliability compared to relay-based transfer switches.
Let’s see what makes iSTS devices a superior a transfer switch and a wise investment:
Faster transfer times. The fully solid-state switching components (thyrsitors / SCRs) have transfer times of less than 1 msec and under worst case conditions, up to 5msec (1/4 cycle), which is suitable for even the most sensitive equipment.
No moving parts in the switching circuits. The solid-state thyrsitors have no moving parts and therefore are impervious to wear and tear.
Safe for overload and high fault currents. iSTS devices have at least 200% to 400% continuous over capacity for robustness and reliability, featuring generously overrated components as well as internal fuses for added protection.
Synchronous transfers that always occur at zero current. This is true for both steady state and transient levels.
Load faults are not transferred.
Thyristor / SCR open and short circuit protection.
No single points of failure in the switching circuit. iSTS models have redundant fans, power supplies and monitoring, voltage sensing of all inputs and outputs.
The switching circuits work independently of the control hardware. Because the switching doesn’t rely on microprocessors, it is safe guarded against failures.
We manufacture iSTS products to be adaptable to suit your unique requirements, with flexible input and output configurations and global compatibility with all region specific AC frequencies and voltages.
We understand the challenges faced when managing critical power so we’ve engineered our iSTS products to address these issues.