0015-D17V4 PLC Application Notes
- 1. Surge Protection for SCADA and Process Control Application Note Tristan King
- 2. Novaris Pty Ltd 33 061 301 88 novaris.com.au sales@novaris.com.au Page 1 Document No: 0015-D17V4 72 Browns Rd, Kingston TAS, AUSTRALIA 7050 Tel +613 6229 7233 Fax +613 6229 9245 Introduction SCADA and process control equipment, such as Programmable Logic Controllers (PLCs), Remote Terminal Units (RTUs) and associated switching and metering equipment contain sensitive electronics, and therefore are at a high risk of damage in the event of electrical surges. Furthermore, the equipment itself and the downtime necessary to repair and replace damaged equipment can become very costly. When designing a lightning protection system, the SCADA and other control equipment must be given special consideration to minimize the risk of damage and system downtime. Novaris has engineered a range of products intended to minimize the risk to process control equipment in the event of an electrical surge, whilst not affecting the operation of the equipment. The level of protection provided, and the correct operation of equipment is dependent upon selecting the correct surge protective device (SPD) for the application. This document is intended to aid in selecting the correct SPD for a variety of different applications commonly found in process control, and to pr4ovide the designer with information as to where SPDs should be installed. For advice please contact your local Novaris distributor or visit the Novaris website. Overview To provide adequate protection, SPDs are needed at either end of any significant cable run in the system. An SPD, such as a Novaris SLT threaded signal line protectors should be installed into instrument enclosures, utilising a spare gland thread. The PLC or RTU end of the cable run should have an SPD such as a Novaris SL slimline signal line protector fitted; the SPD can replace the marshalling terminals. For hazardous areas, and in the case of intrinsically safe circuits, the placement of SPDs is very similar to conventional process control, with the added concern of protecting the safety barrier. Novaris intrinsically safe surge protectors should be installed as shown in figure 1. Figure 1: Installation of SPDs for Hazardous areas
- 3. Novaris Pty Ltd 33 061 301 88 novaris.com.au sales@novaris.com.au Page 2 Document No: 0015-D17V4 72 Browns Rd, Kingston TAS, AUSTRALIA 7050 Tel +613 6229 7233 Fax +613 6229 9245 Surge protection must also be considered between the PLCs and the supervisory computer system and human machine interface (HMI). As with PLCs and field instruments, an SPD must be installed at each end of any significant cable run. Novaris SL slimline signal line protectors are suitable for all common signal protocols used in process control. Analogue and Digital Inputs / Outputs Surge protection requirements for analogue and digital inputs / outputs are almost identical. Figure 2 shows how to effectively protect 24V digital inputs and outputs with a current less than 250mA and low frequency (<250 kHz) ±24V signals. Cabinet earth SL-36-G Marshalling/System Cabinet Instrument Enclosure SLT1-36-M/NXX L1 L2 E1 E2 PLC/SCADA I/O + I/O - Figure 2: Surge protection for Analogue and Digital I/O with isolated DIN rail The location and installation of process control SPDs is the same for all voltage ranges from 5V to 110V, however different models of SPD are required. Refer to Table 1 (page 13) for the applicable surge protection devices.
- 4. Novaris Pty Ltd 33 061 301 88 novaris.com.au sales@novaris.com.au Page 3 Document No: 0015-D17V4 72 Browns Rd, Kingston TAS, AUSTRALIA 7050 Tel +613 6229 7233 Fax +613 6229 9245 Up to 6A Signals In situations where the current draw is greater than the SL-** series rating of 250mA, the SSP6A range is recommended which will pass up to 6A. Figure 3 shows an installation that can handle up to 6A. The SLTs are a shunt connected device and therefore its use is not dependant on the load current. Refer to Table 1 (page 13) for the applicable surge protection devices. Cabinet earth SSP6A-26-G Marshalling/System Cabinet Instrument Enclosure SLT1-36-M/NXX L1 L2 E1 E2 PLC/SCADA I/O + I/O - Figure 3: Surge protection for up to 6A current 4-20mA instrument loops Analogue 4-20mA loop protection is achieved by employing a combination of the SL-420 slimline protector and the SLT1-36-M20 threaded protector as shown in Figure 4. The SL-420 utilises a LED to indicate loop power and surge protection status. Refer to Novaris application note 0015-D31V1 for details of the SL-420i instrument loop protector. As the application note explains, the SL-420i provides some significant advantages over the standard SL-420. Cabinet earth SL-420-G Marshalling/System Cabinet Instrument Enclosure SLT1-36-M/NXX L1 L2 E1 E2 PLC/SCADA I/O + I/O - Figure 4: Surge protection for a 4-20mA instrument loop
- 5. Novaris Pty Ltd 33 061 301 88 novaris.com.au sales@novaris.com.au Page 4 Document No: 0015-D17V4 72 Browns Rd, Kingston TAS, AUSTRALIA 7050 Tel +613 6229 7233 Fax +613 6229 9245 Interposing Relays Due to the isolation provided by an interposing relay, both the digital output from the PLC and the power source can be protected using a single SPD. The example in Figure 5 shows an SSP protecting the power supply, the digital output on the PLC and the interposing relay. Cabnet earth SSP6A-26-G Marshalling/System Cabinet Instrument Enclosure SLT1-36-M/NXX L1 L2 E1 E2 24VDC PS 24V + 0V - CH 0 PLC/SCADA InterposingRelay 6A Figure 5: Interposing relay protection
- 6. Novaris Pty Ltd 33 061 301 88 novaris.com.au sales@novaris.com.au Page 5 Document No: 0015-D17V4 72 Browns Rd, Kingston TAS, AUSTRALIA 7050 Tel +613 6229 7233 Fax +613 6229 9245 Residual Temperature Devices The operation of residual temperature devices is somewhat different to other analogue inputs, in that they work on a change in impedance, and use lower signal levels. There are three common configurations of RTDs, each outlined below with a recommended method of protecting them. 4 wire RTD Figure 6 shows how to effectively protect a 4 wire RTD. Two SL-RTDs are used on the input to the control or PLC, and a SLT4-RTD is installed inside the instrument enclosure. Please refer to the product installation manuals for further detail. Cabinet earth SL-RTD-G Marshalling/system cabinet Instrument Enclosure SLT4-RTD-M/NXX RTDControl Instrumentation Or PLC L1 L2 E1 E2 L1 L2 E1 E2 Figure 6: Surge protection wiring for a 4 wire RTD
- 7. Novaris Pty Ltd 33 061 301 88 novaris.com.au sales@novaris.com.au Page 6 Document No: 0015-D17V4 72 Browns Rd, Kingston TAS, AUSTRALIA 7050 Tel +613 6229 7233 Fax +613 6229 9245 3 wire RTD Figure 7 shows how to effectively protect a 3 wire RTD. Two SL-RTDs are used on the input to the control or PLC, and a SLT4-RTD is installed inside the instrument enclosure. Please refer to the product installation manuals for further detail. Cabinet earth SL-RTD-G Marshalling/system cabinet Instrument Enclosure SLT4-RTD-M/NXX RTDControl Instrumentation Or PLC L1 L2 E1 E2 L1 L2 E1 E2 Figure 7: Surge protection wiring for a 3 wire RTD
- 8. Novaris Pty Ltd 33 061 301 88 novaris.com.au sales@novaris.com.au Page 7 Document No: 0015-D17V4 72 Browns Rd, Kingston TAS, AUSTRALIA 7050 Tel +613 6229 7233 Fax +613 6229 9245 2 wire RTD Figure 8 shows how to effectively protect a 2 wire RTD. An SL-RTD is used on the input to the control or PLC, and a SLT4-RTD is installed inside the instrument enclosure. Please refer to the product installation manuals for further detail. Cabinet earth SL-RTD-G Marshalling/system cabinet Instrument Enclosure SLT4-RTD-M/NXX RTDControl Instrumentation Or PLC L1 L2 E1 E2 Figure 8: Surge protection wiring for a 2 wire RTD HART over 4-20mA loops The addition of HART protocol on 4-20mA loops significantly increases the maximum frequency of the signal, and therefore the SPDs need to be capable of passing the signal. Figure 9 shows how to effectively protect combined 4-20mA loops and HART. Cabinet earth SL-DH-G Marshalling/System Cabinet Instrument Enclosure SLT1-36-M/NXX L1 L2 E1 E2 PLC/SCADA I/O + I/O - Figure 9: combined 4-20mA & Hart
- 9. Novaris Pty Ltd 33 061 301 88 novaris.com.au sales@novaris.com.au Page 8 Document No: 0015-D17V4 72 Browns Rd, Kingston TAS, AUSTRALIA 7050 Tel +613 6229 7233 Fax +613 6229 9245 Multidrop HART may be protected in the same manner, with a Novaris SL-DH or Novaris SLT1-36 at the end of every significant cable run (depending on which model of SPD is easier to install). The termination for multidrop HART will be very similar to HART over 4-20mA loops. RS232, RS422 & RS485 Signals RS232 and RS422/485 signals are significantly faster in nature than other digital I/O signals, and therefore raise the maximum operating frequency. The SPDs used must be capable of passing the higher frequency signal. Surge protection for Profibus or Modbus, should be done in the same manner as the data link layer and physical layer protocol used. RS232 Figure 10 shows how to effectively protect a simple three wire signal such as RS232 using Novaris SL- DH SPDs. Cabinet earth SL-DH-EC90 Marshalling/System Cabinet L1 L2 E1 E2 PLC/SCADA RX TX Common Cabinet earth SL-DH-G Marshalling/System Cabinet L1 L2 E1 E2 PLC/SCADA TX RX Common SCN SCN Figure 10: surge protection for RS232 Multidrop RS232 may be protected in the same manner, with a Novaris SL-DH at the end of every significant cable run. The termination for each wire will be very similar to point to point RS232. The multiport RS422 network (figure 10) is equally applicable by substituting SL485-EC90 protectors for SL-DH-EC90.
- 10. Novaris Pty Ltd 33 061 301 88 novaris.com.au sales@novaris.com.au Page 9 Document No: 0015-D17V4 72 Browns Rd, Kingston TAS, AUSTRALIA 7050 Tel +613 6229 7233 Fax +613 6229 9245 RS485 Figure 11 shows how to protect a point to point RS485 signal using Novaris SL485-EC90 surge protectors. Note that only one side of the screen should be terminated to equipment. Refer to Novaris application note 0015-D31V1 for details of the SL-485i RS485 protector. As the application note explains, the SL-485i provides some advantage over the standard SL-485. Cabinet earth SL485-EC90 Marshalling/System Cabinet L1 L2 E1 E2 PLC/SCADA TX/RX TX/RX Screen Cabinet earth SL485-EC90 Marshalling/System Cabinet L1 L2 E1 E2 PLC/SCADA TX/RX TX/RX Screen SCN SCN SCN SCN Figure 11: surge protection for RS485
- 11. Novaris Pty Ltd 33 061 301 88 novaris.com.au sales@novaris.com.au Page 10 Document No: 0015-D17V4 72 Browns Rd, Kingston TAS, AUSTRALIA 7050 Tel +613 6229 7233 Fax +613 6229 9245 Multidrop RS485 Multidrop RS485 may be protected in the same manner, with a Novaris SL485-EC90 at the end of every significant cable run. The termination for each wire will be very similar to point to point RS485. Figure 12 shows an example of how a multidrop RS485 network may be configured and how to protect it. Note that only one side of the screen should be terminated to equipment. Cabinet earth SL485-EC90 Marshalling/System Cabinet L1 L2 E1 E2 PLC/SCADA Tx/Rx+ Tx/Rx- Screen SCN SCN Cabinet earth SL485-EC90 Marshalling/System Cabinet L1 L2 E1 E2 PLC/SCADA Tx/Rx+ Tx/Rx- Screen Cabinet earth SL485-EC90 Marshalling/System Cabinet L1 L2 E1 E2 PLC/SCADA Tx/Rx+ Tx/Rx- Screen SCN SCN SCN SCN Cabinet earth SL485-EC90 Marshalling/system cabinet L1 L2 E1 E2 L1 L2 E1 E2 Tx/Rx+ Tx/Rx- ScreenSCN SCN SCN SCN Tx/Rx+ Tx/Rx- Figure 12: surge protection for Multidrop RS485
- 12. Novaris Pty Ltd 33 061 301 88 novaris.com.au sales@novaris.com.au Page 11 Document No: 0015-D17V4 72 Browns Rd, Kingston TAS, AUSTRALIA 7050 Tel +613 6229 7233 Fax +613 6229 9245 RS422 Figure 13 shows how to protect a point to point RS422 signal using Novaris SL485-EC90 surge protectors. This is a duplication of the RS485 protection. Note that only one side of the screen should be terminated to equipment. Cabinet earth SL485-EC90 Marshalling/system cabinet L1 L2 E1 E2 L1 L2 E1 E2 Cabinet earth SL485-EC90 Marshalling/system cabinet L1 L2 E1 E2 L1 L2 E1 E2 Tx+ Tx- Rx+ Rx- Screen Rx+ Rx- Tx+ Tx- ScreenSCN SCN SCN SCN SCN SCN SCN SCN Figure 13: Surge Protection for RS422 Multidrop RS422 may be protected in the same manner, with a Novaris SL485-EC90 (Figure 10) at the end of every significant cable run. The termination for each wire will be very similar to point to point RS422.
- 13. Novaris Pty Ltd 33 061 301 88 novaris.com.au sales@novaris.com.au Page 12 Document No: 0015-D17V4 72 Browns Rd, Kingston TAS, AUSTRALIA 7050 Tel +613 6229 7233 Fax +613 6229 9245 Ethernet & Industrial Ethernet Industrial Ethernet is becoming increasing popular as the data link layer protocol in process control and SCADA systems, often forming the link between PLCs and RTUs, and the supervisory system and HMI. Surge protection should be considered for all significant cable runs in a network. Figure 14 shows a cabled network with 4 remote nodes and surge protection. A Novaris UTP-RJ45- 24CAT 6 is used to protect the network switch, and Novaris UTP-RJ45-1CAT6 SPDs are used at each remote node. This protection is suitable for any network using a CAT5, CAT5e, CAT6 or PoE physical layer, including Modbus-TCP, PROFINET IO as well as standard local area computer networks. UTP-RJ45-1CAT6 Marshalling/System Cabinet Network Equipment UTP-RJ45-1CAT6 Marshalling/System Cabinet Network Equipment UTP-RJ45-1CAT6 Marshalling/System Cabinet Network Equipment UTP-RJ45-1CAT6 Marshalling/System Cabinet Network Equipment Computer/Communications Rack Network Switch UTP-RJ45-24CAT6 Figure 14: Surge protection for ethernet It is unnecessary to install surge protection on significant fiber-optic or wireless links, as neither are electrical cabling and therefore are not prone to induced surges.
- 14. Novaris Pty Ltd 33 061 301 88 novaris.com.au sales@novaris.com.au Page 13 Document No: 0015-D17V4 72 Browns Rd, Kingston TAS, AUSTRALIA 7050 Tel +613 6229 7233 Fax +613 6229 9245 Quick Reference Signal/Protocol PLC/Cabinet Meter/Instrument ±5V Analogue or Digital SL7V5-G or SSP6A-14-G SLT1-7V5-M/NXX ±12V Analogue or Digital SL18-G or SSP6A-14-G SLT1-18-M/NXX ±24V Analogue or Digital SL36-G or SSP6A-26-G SLT1-36-M/NXX ±48V Analogue or Digital SL68-G or SSP6A-65-G SLT1-68-M/NXX ±110V Analogue or Digital SSP6A-130-G SDT2-130-M/NXX 4-20mA Loop SL420-G (also SL420i-G) SLT1-36-M/NXX 4 Wire RTD 2 x SL-RTD-G SLT4-RTD-M/NXX 3 Wire RTD 2 x SL-RTD-G SLT4-RTD-M/NXX 2 Wire RTD SL-RTD-G SLT4-RTD-M/NXX HART SL-DH-G SLT1-36-M/NXX RS232 SL-DH-G SL-DH-EC90 RS485 SL485-EC90 (also SL485i-EC90) SL485-EC90 RS422 2 x SL485-EC90 2 x SL485-EC90 Profibus DP SL485-EC90 SL485-EC90 Profibus PA SSP6A-38-G SSP6A-38-G Profinet UTP-RJ45-24CAT6 UTP-RJ45-1CAT6 Modbus Check physical layer Check physical layer Modbus – TCP UTP-RJ45-24CAT6 UTP-RJ45-1CAT6 Industrial Ethernet Network UTP-RJ45-24CAT6 UTP-RJ45-1CAT6 Computer Network (Ethernet) UTP-RJ45-24CAT6 UTP-RJ45-1CAT6 Table 1: Signal protection reference table SLTs (Threaded Signal Line Protectors) are manufactured with M20, N12 (1/2” NPT), N34 (3/4” NPT) and other threads available upon request. Please consult your local supplier or Novaris for intrinsically safe models of the listed SPDs