Current Regulatory and Industry Updates for Surge Protective Devices (SPD)

Transcription

1 Surge Protective Devices Current Regulatory and Industry Updates for Surge Protective Devices () A summary of the new NEC guidelines for emergency facilities and renewable energy applications.

2 The 2008 and 2014 National Electric Code (NEC ) guidelines have expanded the requirements for where surge protection devices () must be used to include emergency facilities and renewable energy applications. Since their proper function can be critical in an emergency or for the proper operation of the electrical grid, it is important that the correct type of be specified for these applications, so the methods used to test their operation are important. Anatomy of a Surge Electrical surges can cause disruptions in computer signals and microprocessors, degradation of component junctions that cause random, delayed failure, or instant damage to electrical components. A power surge, or transient voltage, is an increase in voltage significantly higher than the designated level in a flow of electricity. In the United States, standard voltage for residential and commercial structures is 120 volts. When the voltage rises above this level, damage can occur to sensitive electronic equipment. While lightning might be thought to be the major cause of electrical surges, it actually is one of the least common. Fully 80 percent of surges are caused by internal disturbances, such as load switching, variable frequency drives, lighting and HVAC systems. Even though surges from internal disturbances are usually relatively low in intensity, they can add up over time, weakening the sensitive circuitry in today s electronic devices. External disturbances, like surges from utility line switching or lightning, occur far less frequently than internal surges, but their strength can be devastating. When lightning strikes close to power lines, the electrical energy can boost electrical pressure by millions of volts. s are designed to act like pressure-sensitive valves, diverting this extra current to ground. Microvaristor Zinc oxide Intergrandular boundary µm At the heart of many s are metal oxide varistors (MOV) that have a crystalline structure inside, containing zinc oxide. When exposed to over voltage, or a transient surge, the varistors switch from a nearly open state to a clamping state. This is enough to bridge the gaps within the crystalline structure and the MOV becomes an active part of the circuit, providing an attractive path to ground, protecting the equipment downstream. 2

3 Turn-on Voltage: This is the level at which the MOV begins to activate. Clamping Voltage (also referred to as let-through voltage ): This specifies the voltage that will be seen by the downstream (connected) equipment. Clamping voltages vary and are directly dependent upon the magnitude of the surge seen by the. Using the UL rd Edition VPR (Voltage Protective Rating) surge value of 6kV/3kA, a good clamping voltage for a 120V system would be 700, or 800 volts. A lower clamping voltage indicates better protection. Source Eliminated Voltage 1,500v... Clamped Voltage 150v... Turn on Voltage Emergency Systems Surge Protection Load Both the NEC (in the 2008 and 2014 NEC ) and National Electrical Manufacturers Association (NEMA ) specify that s must be used for each voltage level of the facility s service entrance and distribution panels: NEC Article (D): Surge protection devices shall be provided at all facility distribution voltage levels NEC Article 700.8: A listed shall be installed in or on all emergency switchboards and panel boards. NEC Article (B) (1): Where listed equipment, such as a, is provided with specific instructions on minimum conductor sizing, the ampacity of the tap conductors supplying that equipment shall be permitted to be determined base on the manufacturer s instructions. Wind Electrical System Protection The 2014 NEC also specifies that s must be incorporated into wind-powered electrical supply systems to prevent damage from surges. NEC Article (D) states: A shall be installed between a wind electric system and any loads served by the premises electrical system. New NEC guidelines have been established to identify critical operations power systems (COPS) and to increase protection and reliability of the power infrastructure for critical facilities. Critical facilities include any entity that, if damaged, might disrupt national security, the economy, public health or safety. Obvious critical facilities would include: Law enforcement Fire departments Military installations Hospitals, doctors offices Financial institutions Water and wastewater Airports and air traffic control Traffic light systems All government agencies 3

4 Types of Surge Protection Devices Type 1 Line Side A Type 1 is a permanently connected, hard-wired that can be installed on the line side of the main service disconnect. This type of is safe by itself and does not require external over-current protection. s for mounting at Service Entrance s for mounting on Panelboards Type 2 Load Side A Type 2 is a permanently connected, hard-wired intended for installation on the LOAD side of the service disconnect over-current device, including s located at the branch panel. They are not safe by themselves, and require an external fuse or breaker to trip to safely remove them from the circuit. s for protection of downstream equipment Type 3 Type 3 are point of utilization s, installed a minimum of 10 meters (30 feet) from the electrical service panel, for example cord connected, direct plug-in (DPI), receptacle type and s installed at the utilization equipment being protected. Type 4 Type 4 are component s, including discrete components as well as component assemblies. They consist of one or more Type 5 components assembled together with a disconnect (integral or external) as a means of complying with the limited current tests. Component s Type 5 Type 5 s are discrete component surge suppressors (such as MOVs) that may be mounted on a printed circuit board, connected by its leads or provided within an enclosure with mounting means and wiring terminations. 4

5 Ensuring Proper Function Surge Protection Devices are available in a range of ratings, depending on the level of protection needed. They are used to insure that electrical surges do not cause damage to sensitive electronics. Higher surge ratings provide a higher level of protection and greater redundancy for ensuring a longer useful life. However, like any insurance policy, the higher the level of protection specified, the higher the cost. The ratings used to classify s can be determined in two ways: Calculated: The surge rating is the sum of all the MOVs in a given mode or phase; three 50kA MOVs A-N would be 150 ka per mode. However, this does not take into account design elements that may reduce the surge protection in real world conditions, such as printed circuit board traces used as surge current carrying paths in the design of the. Additional Resources Here are some additional resources about the new NEC guidelines for surge protection in emergency facilities and renewable energy applications: The NEMA Surge Protection Institute (NSPI) is an educational outreach effort initiated by the Low Voltage Surge Protective Devices Section of the National Electrical Manufacturers Association (NEMA). A listing of each state and the status of NEC adoption. Independently verified: An independent testing labora tory tests the under real-world conditions to measure the true protection capacity. This ensures the will deliver the level of protection it claims. Considering the importance of the COPS facilities being protected, a third-party laboratory should independently test any used in these applications. 5

6 AC Voltage Applications and Location Guide IEEE C Category C IEEE: Category C Service Entrance Exposure NEC 285 & NRTL: Type 1, 2, or equivalent Type 4 N&G Bonded (i.e., L-N and L-G are same) Higher available fault currents require appropriate SCCR ratings Historical ka ratings: Per Phase: 400kA to 200kA per phase Per Mode: 200kA to 100kA per mode (Per Phase generally considered Sum of L-N plus L-G) Line Side Load Side Surge Current ka ratings for all Categories are subjective. Consult mfg for specific recommendations Type 1 Line side requires Type 1 per NEC 285 & UL 1449 Service Entrance UL 96A Lightning Protection System s at Service Entrances require 20kA I-n and UL Mark IEEE: Category B External remnant or Internally Induced Distribution IEEE C Category B NEC 285 & NRTL: Type 1, 2, or equivalent Type 4 L-N and L-G are different need L-N, L-G, and N-G Require appropriate SCCR ratings Historical ka Ratings: Per Phase: 300kA to 100kA per phase Per Mode: 150kA to 50kA per mode (Per Phase generally considered Sum of L-N plus L-G) Wind or PV Generation Indoor HVAC (VFD) Equipment installed outside of the building could increase exposure level to Category C. Consider effects of Ground Potential Rises from direct lightning strikes to earth. Type 1 or 2 Lighting Indoor Type 1 or 2 IEEE C Category A IEEE: Category A, maybe B, maybe C if outdoor loads are connected NEC 285 & NRTL: Type 1, 2, or equivalent Type 4. Could be Type3. L-N and L-G are different need L-N, L-G, and N-G Require appropriate SCCR ratings Historical ka Ratings; Per Phase: 160kA to 100kA per phase Per Mode: 80kA to 50kA per mode UPS (or PDU, PDM) Branch Pre (Type 1) Post Indoor Lighting Branch (Per Phase generally considered Sum of L-N plus L-G) Computers or Servers Lighting 6 Revision Date: April 14, 2014 Images depected herein are for demonstration purposes. Each facility is different and user needs may vary. Adjust accordingly, based on equipment value and/or downtime expenses.

7 Provided by NEMA ATS / STS Gen Set Load side of the Switch protects Service and Gen Set Relevant Standards (1000V and Less): ANSI/UL 1449 Surge Protective Devices UL 1283 EMI/RFI Filtering ANSI/IEEE C Guide on Surge Environment ANSI/IEEE C Characterization of Surges ANSI/IEEE C Testing IEEE C Testing IEEE C Application Guide Distribution MCC Busway HVAC (VFD) Protect both ends of the busway against reflections Establishes a new reference to ground, like a service entrance. L-N only may be sufficient Type 3 Separately Derived System Small or Office Equipment Branch Indoor Branch Equipment Equipment Type 1 or 2 Series Equipment Equipment installed outside of the building could increase exposure level to Category C. Consider effects of Ground Potential Rises from direct lightning strikes to earth Series or two-port s may disconnect downstream loads at end of life 7

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