The Use of Surge Protection Devices in the Petroleum/Petrochemical Industry

Transcription

1 The Use of Surge Protection Devices in the Petroleum/Petrochemical Industry Copyright Material IEEE Paper No. PCIC-97-9 Tom Mueller Cutler-Hammer Surge Products Abstract: Without clean power, petroleum and petrochemical equipment is subject to possible upset or catastrophic failure. To cost-effectively eliminate power disturbances due to lightning, fast ringing transients and electrical noise, the use of surge protection devices at building entrance feeders, key branch panels, critical loads and communication lines is recommended. Their use improves the operating reliability of electronic equipment. Index Terms: surge protection, clean power, electrical power distribution. Introduction Dirty Power is preventing facility operators from realizing the increased efficiencies expected from investments in automation and process control equipment. Surge Protection Devices (SPD), also known as Transient Voltage Surge Suppressers (TVSS), are one technology that improves electronic equipment productivity and uptime. Their effectiveness to protect against transients and electrical noise has made SPDs the fastest growing new technology in the electrical industry (see Figure 1: Growing Demand for Pure Power). Surge suppressors Power-conditioning equip. Electronic ballasts Fire/security alarm system. Variable speed drives Energy efficient motors Solid-state motor controls Programmable logic cont. Voice/data cable system. Power-Monitoring system. N ew Technology products thathave been bought,specified or installed in the previous two years by engineers/contractors (n=1443 responses) FIGURE 1. Growing Demand for Pure Power This paper is intended to: outline why microprocessor and solid state devices used in modern petroleum and petrochemical facilities are susceptible to power disturbances; provide an outline of how power disturbances affect the reliability of electronic equipment; David Graff Cutler-Hammer Canada detail a methodology for implementing facility wide power protection systems; and, highlight the installation factors that maximize sensitive load protection. Protecting a facility against transients and electrical noise requires the installation of SPD devices at building entrance feeders and branch panels or next to critical loads. This cascaded protection approach reduces high and low energy disturbances to levels where component damage and degradation and process disruption are minimized. In applications where external data/phone/cable lines enter a facility or ground loop problems exist, surge protection devices can prevent damaging power disturbances. The power quality disturbance, technology and protection terms used in this paper are defined in Table I: Definitions. The Sensitivity of Electronic Equipment Is Increasing In 1993 power related problems cost U.S. companies an estimated $26 billion [4] a year in lost time and revenue. The cost continues to grow because microprocessor based devices are becoming more sensitive and their use is increasing as forecast by the Electric Power Research Institute (EPRI). EPRI projects that by the year 2000, 60 to 70 percent of total utility power generated within the U.S.A. will be controlled by power electronics. This compares with 30 percent in 1995 [5]. Disturbances such as electrical noise or transients, with magnitude equal to two times the rated operating voltage, can threaten the operation of microprocessor-based equipment, create downtime and reduce productivity (see Table II: Effect of Electrical Noise and Transient Disturbances). Disturbances less than two times operating voltage also create problems. An example is electrical noise: the logic voltage signal of an electronic circuit can be swamped and cause operation errors and equipment downtime (see Figure 2: Effect of Electrical Noise on Microprocessor Operation). TABLE I Definitions [1,2] TP T.E. 1

2 Definitions Comments Surges; Spikes; Transients Noise Swell Sag Over Voltage Under Voltage Interruptions An over voltage (or under voltage) condition with a duration of less than half cycle of the normal voltage wave form of either polarity. Unwanted electrical signals which produce undesirable effects in the circuits of sensitive electronic equipment. An increase in the RMS nominal voltage (120VAC) at the normal power frequency (60Hz) for duration of a half cycle to a few seconds. A decrease in the RMS nominal voltage (120VAC) at the normal power frequency (60Hz) for duration of a half cycle to a few seconds. Sustained swell; duration of more than a few seconds. Sustained SAG; duration of more than a few seconds. The complete loss of voltage for a period of time. Detectable only by sophisticated power analyzers, these disturbances result in direct component damage or deterioration. Due to lightning, switching/cycling loads. More commonly known as low magnitude, high frequency disturbances; affect equipment operation. Created by motor generators, variable frequency drives, and other electronic equipment. Usually due to large loads shutting down or utility faults (eg. Large motors coming off line). Often a noticeable increase in light brightness. Due to large loads coming on line and utility faults (e.g.: motors, welders, power factor capacitors). Often a noticeable dimming of lights. Noticeable in lights. Due to large loads, utility faults, improper wiring. Noticeable in lights. Due to large load startup, poor distribution wiring, utility faults. No specific time frame is specified. TABLE II Effect of Electrical Noise and Transient Disturbances [6] TP T.E. 2

3 Im pactto Electronic Loads Im pulse 4x Normal Im pulse 2x Normal Repetitive Disturbance (noise) Circuit Board Failure Yes Yes Data T ransmission Errors Yes Yes Yes Memory Scramble Yes Yes Yes Hard Disk Crash SCR Failure Yes Yes Process Interrupt Yes Yes Yes Power Supply Failure Yes Yes Program Lock Up Yes Yes Yes TP T.E. 3

4 Noise 20-30V logic signal Noise Most industrial environments are susceptible to power transients or spikes. To help ensure fault free operation and protection of equipment, we recommend surge suppression devices on power to the equipment in addition to isolation equipment. [7] 3-5V logic signal FIGURE 2. Effect of Electrical Noise on Microprocessor Operation Advances in microprocessor technology have resulted in sub-micron features and more densely packed integrated chips with lower signal voltages to increase operating speed. The decreased signal voltage allows for increasing circuit density; however, the downside is that electronics are more prone to damage or failure. Application and facility engineers responsible for ensuring maximum up-time and productivity cannot count on past experience when designing modern day process control environments. The greater susceptibility of electronic loads makes past practices and experience only partially relevant. Maximizing the productivity of modern day facilities requires the use of cost effective surge protection. Based on field operating experience, manufacturers of electronic equipment recommend the use of surge protection devices (see Table III: Manufacturer SPD Recommendations). Elements of a Quality Surge Suppression Device The SPD design and performance criteria that ensure high levels of protection and reliability include surge current rating, filter performance, the Underwriters Laboratories (UL) assigned Suppression Voltage Rating (SVR), internal fusing, monitoring and the quality of internal construction. Two types of surge protection devices are commonly used: parallel and series surge protectors. Series SPDs utilize inductors that enhance their ability to reduce power disturbances to levels lower than those achieved by parallel design SPDs. Series filters are not cost effective for large load applications. At higher current ratings, the inductors used in Pi filter networks become large and costly. In contrast, parallel SPDs are not sized to a given current or load and Measures to suppress interference are frequently only taken when the controller is already in operation and reception of a signal has already been affected. The overhead for such measures (e.g. special contractors) can often be considerably reduced by observing the following points when you install your controller. These points include: Physical arrangements of devices and cables; Grounding of all inactive metal parts; Filtering of power and signal cables; Shielding of devices and cables; and, are more cost effective when used to protect a number of loads at the same time. Specifications that ensure SPD reliability and load protection are shown in Table IV: Key Elements of a Quality Surge Protector. Facility Design Methodology Figure 3: Typical Petrochemical Application is an example of a petrochemical facility utilizing electronic equipment. The loads requiring both AC power and/or data/phone/cable protection include the fire alarm system, process control equipment, PCs, UPS systems, drives and even electronic ballasts. Eighty percent of all disturbances are noise and transients generated by loads within the facility. The remaining 20 percent of disturbances are caused by external forces such as lightning and utility faults. The design and implementation of a power protection solution for petroleum and petrochemical facilities is developed using the following two principles: the Power Quality Pyramid; and, the implementation of a cascaded network of protection. The Power Quality Pyramid Ensures Cost Effective Power Quality Solutions: Grounding is the basis of the pyramid and the foundation of reliable power systems (see Figure 4: Power Quality Pyramid). Poor or improper grounding typically causes 80 percent of all power quality problems. TABLE III Manufacturer SPD Recommendation TP T.E. 4

5 M M M M M FIGURE 3. Typical Petrochemical Application TP T.E. 5

6 TABLE IV Key Elements of a Quality Surge Protector Key Elements Recommended Specification Target 1. Surge Current Per Phase Appropriate sizing for long term protection 2. Integrated Installation Lowest possible let through voltage; no contractor/installation problems; eliminates horizontal wall space 3. Effective Filter Dampens internal ringing transients/noise the most common transient 4. Low Let Through Voltage Key performance measurement 5. Internal Fusing System Safety and overcurrent protection 6. Reliable Monitor and Diagnostics System Foolproof status indication 7. Quality Construction Ability to achieve quoted performance 250 ka/phase (building entrance feeder); 120 ka/phase (panelboards) TVSS supplied by gear manufacturers TVSS mounted inside low voltage distribution equipment (direct bus bar connection); Switchgear, Switchboards, Panelboards, MCCs, Busway Noise attenuation (exceed khz) Let through voltage result using Cat B3 ringwave (6kV, 100 khz) less than 208V, 480V Let through voltage using C1 (6kV, 3kA) equal to 400V (208V system); 800 V (480V system) 200 kaic internal fusing system Comprehensive monitoring system that does not depend on only the monitoring of fuses or circuit breakers All suppression components mounted directly to solid copper surge plane 3 rd party independent test results verifying quoted surge current ratings TP T.E. 6

7 CP FIGURE 4. Power Quality Pyramid - Effective power quality solutions start with grounding. - IEEE recommends the use of TVSS in a facility-wide design. Cost-effective protection for all solid state loads [2]. - Voltage Regulation has limited applications (analog power supplies; site specific problems). - UPS employed at critical locations (highest $/k VA). IEEE recommends TVSS devices upstream of a UPS [2]. The Power Quality Pyramid also recommends the use of SPDs. Transients and noise can be shunted by surge devices to ground when installed at strategic main and sub-panels, near critical loads and disturbance generating equipment. A Cascaded Network Is Required to Limit High Energy Disturbances: Building entrance feeder surge protection is mandated as per NFPA 780: Devices suitable for the protection of the structure shall be installed on electric and telephone service entrances and on radio and television antenna lead-ins. Electrical systems and utilization equipment within the structure may require further surge suppression. [4]. The concept of a two-stage protection approach is recommended in IEEE s Emerald Book: For large surge currents, diversion is best accomplished in two stages: the first diversion should be performed at the service entrance to the building. Then, any residual voltage resulting from the action can be dealt with by a second protective device at the power panel of the computer room (or other critical loads). [2]. If only building entrance feeder protection were provided, the let-through voltage will be approximately 950V in a 277/480V system exposed to induced lightning surges. This level of let-through voltage can cause degradation or physical damage of most electronic loads. Framework For Applying SPDs for Facility Wide Protection: The system approach views the electrical distribution layout as one system and attempts to maximize equipment reliability and productivity. By identifying the critical, non-critical and disturbance generating loads within a facility, and reviewing the internal power distribution network, a determination of where to install mitigating equipment can be made. The most effective and economic solution for protecting a large number of loads is to install parallel SPDs at the building entrance feeder and panelboard locations. This reduces the cost of protection for multiple sensitive loads can be protected with one device. The recommended methodology is summarized in Figure 6: System Approach for Installing SPDs. 1. Identify Critical Loads 2. Identify Non-Critical Loads 3. Identify Noise and Disturbance Generating Loads 4. Review Internal Power Distribution Layout TVSS Stage 1 Protection (S ervice Entrance) 480V 120/208V TVSS Computer or Sensitive Loads Stage 2 Protection (Branch Location) System T est Parameters: IEEE C62.41[10] and C62.45 [10] test procedures using category; 480V main entrance panels; 100 feet of 3 phase wire; 480/208V distribution transformer; and 208V branch panel. = Hybrid Parallel Suppressor PEAK VOLTAGE 20,000V 800V 400V 0 Input - high energy transient dis turbance; IEEE Category C3 Impulse 20,000V; 10,000A Best achievable performance with single T VSS at main panel S tage 1) 25 us 50 us T IME (MICROSECONDS) Two stage (cascade approach) achieves best possible protection (less than S tage 2 ) 5. Identify Facility Exposure to Expected Levels of Disturbance 6. Apply Mitigating Equipment to: a) Main Panels b) Key Sub-Panels c) Critical Loads d) Data and Communication Lines FIGURE 5. Cascaded Network Protection The benefit of implementing cascaded network protection is shown in Figure 5: Cascaded Network Protection. Combined, the two stages of protection at the service entrance and branch panel locations reduce the IEEE recommended test wave (C3-20kV, 3kA) to less than 200V voltage, a harmless disturbance level for 120V rated sensitive loads. FIGURE 6. System Approach for Installing SPDs There may be critical loads within a facility that require a higher level of protection. Such loads are essential for the health and safety of personnel or responsible for critical TP T.E. 7

8 GROUND GROUND operations within a facility. An example is a computer that controls a processing line/operation. A series SPD is best suited for protecting such loads. Advantages of the System Approach are: the lowest possible investment in mitigating equipment to protect a facility; building entrance SPDs protect the facility against large external transients, including lightning; SPDs are bi-directional and prevent transient and noise disturbances from feeding back within a system when installed at distribution or branch panels; and two levels of protection safeguard sensitive loads from physical damage or operational upset. Integrated SPD Devices Offer Significant Performance Improvements Historically, surge suppression devices were purchased as stand-alone devices and installed next to a panelboard, switchboard or motor control center by an electrical contractor. In 1995 gear manufacturers began integrating SPD devices into electrical distribution equipment to increase the level of protection provided against surge and noise disturbances. Directly connecting the surge suppresser to the bus bar of electrical distribution equipment results in the best possible level of protection. Compared to side mounted devices, connecting the SPD unit to the bus bar eliminates the need for lead wires and reduces the letthrough voltage up to 50 percent (see Figure 7: Integrated SPDs Offer Significant Performance Improvements). Given surges are high frequency disturbances, the inductance of the installation wiring increases the letthrough voltage of the protective device. Figure 8: The Effect of Installation Lead Length on Let-Through Voltage, shows that for every inch of lead length, the let-through voltage is increased by an additional 15V to 25V above the manufacturers stated suppression performance. Lead length has the greatest effect on the actual level of protection realized. Twisting of the installation wires is the second most important installation consideration. By twisting the installation wires, the area between wires is reduced and the mutual inductance affect minimized. A dditionallet-though Voltage Using IE E E C1(6000V,3000A )[3]Waveform (UL 1449 TestW ave)[12] Additional Let T hrough Voltage* FIGURE V (23% ) 673 V (75% ) 3 ft Lead Length 1 ft Lead Length, Loose Wiring T wisted Wires Twisted Wires 14 AW G 10 AW G 4 AW G * Additional to UL1449 ratings The Effect of Installation Lead Length on Let-Through Voltage Increasing the diameter of the installation wires is of negligible benefit. Inductance is a skin effect phenomenon and a function of wire circumference. Since only a marginal reduction in inductance is achieved when the diameter of the installation conductors is increased, the use of large diameter wire results in only minimal improvement. Side m ounted SPD -used for retrofit applications G VS SPD SPD integrated into panelboards, sw itchboards,m C Cs SPD N G Let-Through Bus Bar Y/120 Panelboard (integrated versus side mounted SPD) Surge Event Side mounted SPD device (assuming 14 lead length to bus) Integrated SPD (direct bus bar connecttion) \ N Microseconds FIGURE 7. Integrated SPDs Offer Significant Performance Improvements TP T.E. 8

9 Further benefits provided by integrated surge suppression designs are the elimination of field installation costs and the amount of expensive outboard wall space taken up by sidemounted SPD devices. Building Entrance Feeder Installation Considerations Installing a SPD device immediately after the switch gear or switch board main breaker is the optimal location for protecting against external disturbances such as lightning. When placed in this location, the disturbance is intercepted by the SPD and reduced to a minimum before reaching the distribution and/or branch panel(s). The use of a disconnect switch eliminates the need to deenergize the building entrance feeder equipment should the SPD fail or require isolation for Megger testing. The size or capacity of a suppressor is measured in surge current per phase. Larger suppressors rated at approximately 250kA per phase should be installed at the service entrance to survive high energy surges associated with lightning. A 250kA per phase surge rating allows for over a 25 year life expectancy assuming an IEEE defined high exposure environment [10]. Lower surge rating devices may be utilized; however, device reliability and long term performance may be compromised. For aerial structures, the 99.8 percentile recorded lightning stroke current is less than 220kA. The magnitude of surges conducted or induced into a facility electrical distribution system is considerably lower given the presence of multiple paths for the surge to travel along [10]. It is for this reason that IEEE C62.41 recommends the C3 (20kV,10kA) test wave for testing SPDs installed at building entrance feeders. SPDs with surge ratings greater than 250kA are not required. The incremental benefit is minimal and the additional cost difficult to justify. Installing Panelboard Surge Protection Devices Wherever possible, consultants, specifiers and application engineers should ensure similar loads are fed from the same source. In this way, disturbance generating loads are separated from electronic circuits affected by power disturbances. For example; motor loads, HVAC systems and other linear loads should be separated from the sensitive process control equipment employed within petroleum and petrochemical facilities. Smaller surge capacity SPDs (120kA per phase) are installed at branch panelboards where power disturbances are of lower energy but occur much more frequently. This level of surge current rating should result in a greater than 25 year life expectancy. When isolated ground systems are used, the SPD should be installed such that any common mode surges are shunted to the safety ground. The use of a disconnect switch is optional. The additional let-through voltage resulting from the increased inductance caused by the disconnect switch is about 50V to 60V. This increase in disturbance voltage can result in process disruption and downtime. Motor Control Center and Bus Way Installation Considerations Increasingly, motor control centers (MCC) power VFDs, solid state overload relays, electronic soft starters, electronic metering and relaying equipment require protection from power disturbances. When utilized in building entrance feeder applications, MCC SPDs provide the first stage of protection against external high energy power disturbances. To reduce incoming power disturbances to the lowest level possible, the surge protector should be installed onto the bus bar in the main incoming structure. If there is no room in the main structure, the SPD should be installed in a cell located at the top of the first or second structure. In this fashion, external disturbances are intercepted before entering the facility electrical distribution system. A common convention in the past has been to install lightning arrestors within MCCs used in building entrance applications. The level of protection offered by these devices is inadequate for today s sensitive loads. The typical let-through voltage of a surge arrester using the IEEE C62.41 C1 test wave form (6000V, 3000A) is between 1500V and 2000V. This is a far lower level of protection compared to the 800V let-through voltage for a 480V WYE SPD. Downstream MCCs may include a panelboard feeding electronic loads. In such applications, the SPD can be integrated into the panelboard or between the transformer and panelboard lugs. This prevents power disturbances from affecting the electronic loads connected to the panelboard. In all cases, whether at the building entrance feeder, subfeed or branch locations, the SPD units installed in MCCs should be mounted in a wrapper with stabs to minimize installation lead length, time and cost. In facilities with busway systems, the first stage of protection is typically integrated into the building entrance switch gear. The second stage of protection is a SPD installed in a bus plug with stabs allowing for easy, minimal lead length installation. Surge protection should be placed ahead of any critical loads to prevent the primary stage let-through voltage from disrupting operations. TP T.E. 9

10 Installing Dataline Surge Protection Most petroleum and petrochemical facilities utilize communication lines for process monitoring and control. As identified by the Power Quality Pyramid, proper grounding of communication lines is essential for dependable operation. This concept is seconded by NEC Article 800 which states that all data, power and cable lines be grounded and bonded [11]. Power disturbances such a lightning can elevate the ground potential between two communicating pieces of electronic equipment with different ground references. The result is current flowing through the data cable causing component failure, terminal lock-up, data corruption and interference. NFPA 780 D warns that surge suppression devices should be installed on all wiring entering or leaving electronic equipment, usually power, data or communication wiring [9]. Surge suppressers should be installed at both ends of a data or communication cable. In those situations where one end of the cable is not connected into an electronic circuit (eg. contactor coil), protection on the electronic end only is acceptable. To prevent the coupling or inducing of power disturbances into communication lines, the following should be avoided: data cables should not be run over fluorescent lighting fixtures; data cables should not be in the vicinity of electric motors; the right category cable should be used to ensure transmission performance ; and, data cables must be grounded at both ends when communicating between buildings. References [1] EC&M Reader Survey (1995): New Technology Products that have been bought, specified or installed in the previous two years by engineers/contractors (n=1443 responses) [2] Emerald Book, IEEE Std Recommended Practice for Powering and Grounding Sensitive Electronic Equipment (ANSI) [3] IEEE Std , The New IEEE Standard Dictionary of Electrical and Electronics Terms, Fifth Edition [4] Jane Clemmenson, Collective Intelligence, Santa Rosa, CA, 1993 IEEE Spectrum June 93 [5] Electronic Power Research Initiative (EPRI) [6] Dranetz Field Handbook for Power Quality Analysis, 1991 [7] Allen Bradley SLC500 Operational Manual N1002, Series A, September 1993 [8] Siemens AG Automation Group EWA [9] NFPA 780, Lightning Protection Code, 1992 Edition [10] IEEE Standards Collection, Surge Protection C62, 1995 Edition [11] NFPA 70, National Electric Code 1993 Edition [12] UL 1449: UL Standard for Safety for Transient Voltage Surge Suppressors Summary Electronic loads are critical to achieving competitive levels of production within today s petroleum and petrochemical industry. Their increasing susceptibility makes it necessary to protect them against power disturbances. The Power Quality Pyramid is a framework for implementing facility wide power protection designs. Proper grounding, the use of SPDs at building entrance feeders and branch panel locations using a cascaded network, a facility wide approach and dataline protection to safeguard communication devices, ensures cost effective protection against power disturbances. The level of protection realized is greatest when SPDs are integrated into a facility s electrical distribution equipment. Compared to conventional side mounted SPD installations, integration eliminates the inductance associated with installation wires and results in 50% lower let-through voltages. TP T.E. 10

11 TP T.E. 11