|“I have a UPS, why do I need a TVSS?”
For over 27 years this has been a common objection dealt with on a regular basis. Let me point a few facts about UPS systems and then deal with susceptibility issues and add some comments from IEEE.
The UPS provides for secondary or backup power in the event of loss of utility power. The UPS protects electrical and electronic systems, process controllers and data against the loss of the primary power source which is the utility company.
Many UPS’s incorporate relatively low energy and low pulse life Category A or B surge suppression. This low energy built-in surge suppression may protect the UPS and its connected load from a limited number of small hits, but it should not be relied upon as a transient solution. The Institute of Electrical and Electronics Engineers (IEEE) recognized this problem and stated in Section 9.11 of IEEE Standard that you need networked TVSS protection. We call this the system shield.
Transient Susceptibility of the UPS
Protecting the Electronic UPS
Transient protection is recommended at the input to all electronic loads and the UPS is no exception. The AC-to-DC converter, the static by-pass switch, and to a lesser extent the DC-to-AC inverter, are all susceptible to transient damage. Sensitive and transient susceptible electronic control circuitry constantly monitors the status of the UPS and the input and output AC power of the UPS. This circuitry is used to determine if the UPS should be delivering power from the batteries and DC-AC converter: or, if the UPS should switch to the bypass mode and deliver AC from the secondary source which is usually the utility AC power. Additionally, when the UPS is in the bypass mode for maintenance or due to failure, the sensitive loads should also be protected against transient disruption, degradation, and damage from the transients appearing on the secondary AC source or utility power.
The IEEE Standard 1100-2005 states the networked TVSS protection is needed, and UPS TVSS protection as follows:
Section 9.11 of IEEE Std. 1100-2005: “… A listed and properly rated TVSS should also be applied to each individual or set of electrical conductors (e.g. power, voice, data) penetrating any of the six sides fanning a structure.”
Section 9.12 of IEEE Std. 1100-2005: “… it is recommended that additional TVSS be applied to downstream electrical switch boards and panel boards if they support electronic load equipment.”
UPS surge protection
Section 9.11.3 UPS surge protection: “Lightning and other transient voltage producing phenomena are harmful to most UPS equipment and to sensitive electronic load equipment (e.g. via an unprotected static-switch bypass around the UPS). Therefore, it is recommended practice that both the rectifier-charger input circuit to the UPS and the associated UPS bypass circuits (including the manual maintenance bypass circuit) be equipped with effective Category B TVSS protection as specified in IEEE Std. C62.41-2002…”
IEEE Std. 1100-2005 assumes that anSPD protection network (e.g.SSI®
System Shield) is in place when discussing UPS surge and transient protection.
The requirement that the service entrance and down stream switchboards and panel boards are properly protected with TVSS is assumed to be met. Additionally, Category B TVSS protection is required for the recitifier-charger input circuit and the associated UPS bypass circuits.
Built-in UPS transient voltage suppression
Today, many UPS manufacturers provide low level lightning and surge protection. A typical UPS designed to power a computer may claim the UPS passes ANSI/IEEE C62.41-2002 Category A and/or Category B test waveforms. In general, one would assume that the UPS survives these transients, since there is no pass or fail in the ANSI/IEEE C62.41-2002. The adequacy of this built-in surge suppression to protect the connected load(s), the let-through voltages, the energy handling capability, and the number of hits of a given amplitude for the various transient waveforms that the built-in surge suppression will survive are not in general provided by the UPS manufacturer.
If a protected load is of sufficient value to an organization to protect against power outages with a UPS, the UPS and the vital load should also be protected against transient disruption, degradation, and an SSI suppressor unit placed on line in front of the UPS will protect the investment in the UPS and the connected computer equipment. During maintenance and downtime on the UPS, the SSI unit
will filter out the transients and surges from the line during the static by-pass mode or maintenance by-pass mode of operation, thus protecting the connected computer equipment from damage.
Additionally the majority of the most prominent UPS units do not provide any significant protection for any transients that are transmitted between line and ground. In testing, the residual voltages on a 100kHz Category A transient of 2000 volts injected at 270° on the sinewave as measured on the output of the UPS range from 600 to 1800 volts. This is a significant downside to the idea of utilizing the UPS as a standalone surge protector as well. With the addition of our SPD solution from Surge Suppression Incorporated® will provide complete protection.
Utilizing this combination the UPS itself will benefit with fewer maintenance problems and less downtime.
With the investment in sophisticated computer equipment and a UPS unit, the customer has already committed to keeping the system operational on a continuing basis. The additional investment in the Advantage suppressor by SSI® is minimal by comparison. The additional protection can be significant in terms of preventing even one downtime incident, which at today’s costs can run some companies as much as $78,000 per hour according to studies conducted and published by Computer Technology Review magazine.