TITLE OF THE INVENTION

ICSA distribution transformer monitoring system

The present invention relates to ICSA Distribution Transformer Monitoring System (DTMS) Distribution Transformer Monitoring System is used to monitor and control the Distribution transformers and sub-station feeders The DTMS is also useful in energy audit, load survey and fault analysis This will communicate the alarm conditions, energy parameters and other data to a central control station using a communication link

Applications

Applications of DTMS are

1 ) Extending the life of the distribution transformer This is possible by piotect'ng it from over load, over temperature and protecting from low oil level

2) Increasing the efficiency of the distribution transtoi mer This is possible by balancing the phase loads on transformer

3) Better utilization of imported power at substation This is possible by monitoring power distribution and utilization at transformer level

4) Theft detection This is possible by comparing the consumer metei reading and DTMS reading

5) Easy maintenance If a fuse is blown at transformer Unlit} management gets information with in no time to take corrective action immediately

The DTMS become compact, less power consumption, economical and better integration with mam controller

According to the present invention there is provided Distribution Transformer Monitoring System consisting of

a) 32 bit ARM controller based mother board b) IEC l OI , IEC- ! 04, DNP3, or Modbus protocol support to communicate with mastet

c) Digital outputs with Relays (Potential free contacts) in SBO (Select before Operate) configuration d) Digital inputs (optical isolated), Expandable in nature e) Serial ports (RS232/RS485) to communicate with master and configuration tool

0 Master com' port uses RTS signal with preamble & post amble. g) RTS watch dog for master station communications. h) High accuracy on-board RTC (Real Time Clock) i) Master communication port baud rates configurable with jumper settings. j) LED indications to display Relays and Digital inputs status which LED indication may be visible from see through window on front door, k) The front door of DTMS having locking system. I) Low battery message is provided in case of battery get drained beyond

1 1 V. m) Low battery cutoff is provided in case of battery get drained beyond

10.5V. n) 32K NV RAM for parameter and events storage Expandable in nature o) Front-end software p) Connectors for CT's. q) Onboard Temperature sensor to monitor temperature in DTMS box.

Further according to the present invention the main board consists of 32-bit ARM core based controller.

DTMS have 2 UART serial ports, which can be expanded or multiplexed as per requirement.

RAM module has 32K of external NVRAM to store the Instantaneous parameters and set parameters which are expandable

The module has high accuracy Inbuilt RTC (Real Time Clock). the meter module is interfaced with the Meter module through SPI interface. there are two provided more pseudo digital inputs (DI). the main board has relays for SBO operation, one of them is master relay and other

relays are tor DOs the RTS signal will be disabled when there is no communication tor easy maintenance and trouble shooting test points and LED indications are provided on all digital inputs, digital outputs, communication signals and power supply points

DTMS is very sophisticated monitoring system Refer from fig 1 (Block diagram of DTMS) The DTMS consists of Main board Meter module Power supply, MCB, and Form C connectors for CTs Main board is the heart of the DTMS unit It takes care of the communications (Serial ports), process, timing, memory management, monitor Digital inputs and control Digital Outputs

Communication a) UART To communicate with computers b) SPI To communicate with Meter module

Process Deriving powers and MD from parameters received from metering module and sending them to computer

Timing The micro controller has to check digital inputs status for every l OmSec If the status changed then it will send to computer with time This time has to maintain by controller This is done with the help of an 1C

Memory management To sense the change in digital inputs, the controller needs to know the previous status For this purpose memory is used

Monitor Digital inputs and control Digital Outputs

Main board is connected to meter module with SPI SPI (Serial Peripheral Interface) is a synchronised serial port Main board has 2 serial ports One is to communicate with Master computer and the other is to communicate with configuration utility Configuration utility is software i unning in a computer Main board has provision to connect 8 numbers of Digital inputs and 4 digital outputs

Mater module has a 4 pin connector which accepts 23OV AC +/- 50% The form C connectors connected to meter module Meter module measures voltages, currents and phase angle between voltage & current From the measured values it derives energies and frequency It gives required information to main board

The Power supply gives required DC powers (24V, 12V & two 5.4V) to main board, meter module and wetting voltage to DIs.

We shal l now describe the present invention with reference to accompanying drawings which are given for better understanding of the invention, but do not restrict the scope of the present invention.

Fig I . represents a block d iagram of DTMS Fig 2. gives main board block diagram Fig 3 is a block diagram of meter module Fig 4 (a)- (h ) shows Schematics of main board Fig 5 is a component layout of mainboard Fig 6 (a)- (g) are schematics of meter module Fig 7 is layout of meter module

We shall now describe the invention in detail with reference to accompanying drawings.

MCB is to on off the mains power to DTMS unit. Ref Table 10.2 for connection details.

Main board description CPU

Refer the fig 1 block diagram of DTMS and the fig 2 block diagram of Main board. The main board has 32-bit ARM core based controller. The advantages with ARM controller CPU is very high speed (Up to 60MIPS) still very low power consumption (500 micro amps/MIPS @ 1 .8V), High amount of RAM, ROM and 1Os are built in. The ARM controller CPU is Capability to communicate with various types of serial interfaces (UARTS, 12C, SPl, CAN, and USB). It has JTAG port for debugging the firmware in development stage.

Serial ports (UARTS)

Normally the DI Mb have 2 UART serial ports. These can be expanded or multiplexed as per requirement. One port is used to communicate with master in any one of the protocols (I EC I O l , IEC 104. DNP3. or Modbus). On this port the baud rates (2400/ 4800/9600/19200) and RTS preamble/post ambles (50/100/ 1 50/200 mSec) are configurable with jumper setting. The RTS preamble/post amble and RTS watch dog are useful if the communication is through RF modem. The other port is used to communicate with Configuration Tool running on a laptop/palmtop/PC.

The second serial port is used to communicate with configuration/debugging utility running on a laptop/PC.

RAM

This module has 32K of external N VRAM to store the Instantaneous parameters and set parameters and this can be expandable up to 64MB. This memory may be NV RAM, SDRAM, EEROM, Flash ROM or any combination of these memories.

RTC

This module has high accuracy Inbuilt RTC (Real Time Clock). This is for time stamping and maintaining sequence of events. This gets synchronized with master. The RTC chip is backed with a separate battery to keep correct time for long periods.

Meter module interface and process of Analog parameters

This module is interfaced with the Meter module through SPl interface. The main board is capable to address up to 2 meter modules

With the parameters received from meter module the control ler will derive Active, reactive, & apparent powers, Power factor, and MD. The controller will also accumulate Active (Import, Export) & reactive (Lead, Lag) energies. The MD for last interval 15Min and Current month max. The MD Current month max will get reset at 12.01 AM of next month first. The instantaneous data from this meter module is to be logged periodically and checks for events. The event data will be stored in NV RAM. Some of the event conditions are Current and Voltages are out of dead band levels in any phase, MD of last 1 5 Minutes, and MD of present month.

The MD is calculated in sliding window method Average KVA for one m inute is considered for sliding window Previous 1 5 readings are stored in 15 locations and averaged for month MD calculation These 1 5 readings are compared and highest reading is picked-up for last 15 minute MD These 15 readings are updated tor every minute in FIFO basis I e Oldest minute reading is discarded and latest minute read ing is added to these I 5 readings

The voltage, current and energies are instantaneous values The powers and PF are 2 sec average values The energy accumulation (Counter paiameters) is done in controller

Digital Inputs

The Mam board has optically isolated 8 digital inputs Refer figl block diagram of DTMS The digital inputs are useful to know the status of breakers, Oil temperature, Winding temperatui e of transformer There are another 4 spare digital inputs These inputs are scanned foi eveiy 10msec If any status change is noticed in two successive readings it generates an event with time tag of I mSec resolution The wetting voltage (24V DC) to read potential free contacts is supplied from unit The Lb D indications aie provided to know the status of inputs

There are two more pseudo digital inputs (Dl) They are battery voltage low and Meter board communication failure If the 1 2V battery voltage is below I I V, a pseudo Dl event will be generated If communication failed between meter module and main board a second pseudo Dl event will be generated Using configuration/ debug utility status can be forced/un-forced and events can be enabled/ disabled

Digital outputs

The Main board has 5 relays for SBO operation One of them is master relay and othei relays are for DOs These relays are dual pole relays One pole is for DO operation purpose and other pole is to check the status of the relay The master should send select command The DTMS respond with acknowledgement after successful select operation If select operation failed it will respond with NACK The operate command should come after select acknowledgement If operate command is delayed by set number of seconds then also DTMS will not accepts operate command

In select operation DTMS checks the status of relays. All 5 should be in off state. Then DTMS energizes selected relay. Second time checks the status, now only one selected relay should be in on state and others should be in off state. If the relays in both above checks are in expected states then DTMS sends acknowledgement. After successful select operation, if operate command is received in time then DTMS wil l check third time the status of relays. One selected rela> should be in on state and others should be in off state. If this is OK then master relay wil l be operated. Fourth time checks the status, now both selected relay and master relay should be in on state and others should be in off state. The DTMS wil l off the master and selected relay at a time after given duration of on time. Fifth time checks the status; all 5 should be in off state. If any of the above checks fail then NACK will be sent. The on time will be taken from DNP3 select command. The allowed time delay between select command and operate command is configurable. The range is 1 to 60 seconds. The LED indications are provided to know the status of outputs (Relays).

RTS watch dog

The RTS signal will be disabled when there is no communication. If any master query is received from master the DTMS will first enables (logic 0) the RTS signal. DTMS will wait for preamble time and sends the reply to master. By any reason if RTS held enabled for more than I O seconds (+/- 2 sec) the RTS watch dog will force the RTS to logic 1. RTS watch dog release the RTS when new request received from master. Connectors

For easy maintenance and trouble shooting test points and LED indications are provided on all digital inputs, digital outputs, communication signals and power supply points. Refer Table 3 and Table 4

The metering is done by internal DSP based metering module. Refer from the fig 1 Block diagram of DTMS and fig 3 block diagram of meter module. This is powered from internal isolated power supply. The configuration is 3phase 4 wire (230V phase to neutral and 5aιnp'Max current). The parameters sent by metering module are 3 voltages, 3 currents, 3 energies (Integration time is 0.4micro Sec) and frequency.

Divider Network

Refer the fig 3 Block diagram of meter module. Voltage divider Network. The line voltages are attenuated using a simple Voltage divider network before it is presented to the ADE7758.The maximum signal level permissible at VAP, VBP and VCP is 0.5V peak for the A DF 7758.

Power Supply

Refer the fig 3 Block d iagram of meter module. 5.6 v isolated power supply is used for Meter Module.

Anti aliasing filters

Refer the fig 3 Block diagram of meter module. The need for this filter is that it prevents aliasing. Aliasing is an artifact of all sampled systems. Input signals with frequency components higher than half the ADC sampling rate distort the sampled signal at a frequency below half the sampling rate. This will happen with all ADCs, regardless of the architecture. The combination of the high sampling rate σ-δ ADC used in the ADE7758 with the relatively low bandwidth of the energy meter allows a very simple low-pass filter (LPF) to be used as an anti aliasing filter. A simple RC filter (single pole) with a corner frequency of I O kHz produces an attenuation of approximately 40 dB at 833 kHz. This is usually sufficient to eliminate the effects of aliasing.

Burden Resistor

Refer the fig 3 Block diagram of meter module. Burden resistors arc used for converting CT secondary current to voltage across the secondary winding output. The burden resistor depends on the maximum current (7.5 Amps), the input level to the ADC (50Om V), and the CT ratio being used {1000:1).

Reference IC

Refer the fig 3 Block diagram of meter module This reference IC provides voltage reference (2.5V) to 7758. For this purpose a very accurate (2.5 V+/- 0.001 V) reference IC (ADR42 I BR) is used.

Pulse Output

APCF

Refer the fig 3 Block diagram of meter module. The APCF is Active Power Calibration Frequency (APCF) Logic Output. This APCF" is directly proportional to present active power. This output is used for operational and calibration purposes. This output frequency can provide a simple, single-wire, optically isolated interface to external calibration equipment.

VARCF

Refer the fig 3 Block diagram of meter module. Reactive Power Calibration Frequency Logic Output. It gives reactive power or apparent power information depending on the setting of the VACF bit of the WAVMOD. This output is used for operational and calibration purposes. The full-scale output frequency can be scaled by writing to the VARCFNUM and VARCFDEN registers.

EEROM

Refer the fig 3 Block diagram of meter module. This is used for storing calibration values of Meter IC (ADE7758). Master card reads these values from EEROM and stores into the Meter IC (ADE7758) and gets the parameter data from the Meter Module.

Meter Communication with Master Card:

Refer the fig 3 Block diagram of meter module. The four pins that used in communication are SSEL, MOSI, MISO, and SCK and are described below.

SSEL

Chip Select. Part of the 4-wire serial interface. This active low logic input allows the ADE7758 to share the serial bus with several other devices

MOSI

Data Input for the Serial Interface. Data is shifted in at this pin on the falling edge of SCK

SCK

Serial Clock Input for the Synchronous Serial Interface. Al l serial data transfers are synchronized to this clock. The SCK has a Schmidt-trigger input for use with a clock source which has a slow edge transition time, e.g., opto-isolator outputs.

MISO

Data Output for the Serial Interface. Data is shifted out at this pin on the rising edge of SCK. This logic output is normally in a high impedance state, unless it is driving data onto the serial data bus

Power supply:

Refer the fig 1 block diagram of DTMS. The power supply is SMPS. Input to power supply is 3 ph with neutral (23OV AC +/- 20%) or 1 2V from battery. This gives output even if any one phase is present. This gives Power to entire DTMS including communication modem, wetting supply for potential free digital inputs and battery charges when mains power is present. This Power supply has bui lt in EM I Filter. The battery backup is provided from 12V 4AH Battery. This can give back-up up to 4 Hours continuously. If any of the phases are present battery get charging voltage. When ever phase is present then only DTMS drown power from battery. Low battery message is provided in case of battery get drained beyond 1 1 V. I f battery drained beyond 10.5V, battery low cutoff circuitry will get activated and the battery will get disconnected. The battery remains cutoff until mains ON .

MCB:

Refer fig 1 the block Diagram of DTMS. The MCB is to switch ON/OFF the mains power to unit. It also protects the unit from short circu its. Even though the MCB is switched OFF the boards get required power from battery.

Form C connectors:

Refer the fig I block diagram of DTTMS. There are 9 Form C type connectors used. These are for connecting disconnecting the internal (Secondary) CTs with primary CTs. The primary CTs will be placed out side of DTMS. This primary CTs should not left open for any reason for long time. These Form C connectors have facility to short

the primary CTs when required. To fulfil this function 3 Nos of Form C type connectors need to be used with each CT. For wiring details refer 6.2.9 Terminal Connector.

Main Parts List

Main Board:

• LPC22 I 4 (ARM 7TDMI Microcontroller)

• EPSON RTC (RX-8025 SA) (optional)

• RTC (DS 1 302)

• Watchdog (DS 1232)

• Level Shifter (MAX 232)

• Temperature Sensor (LM 35)

• Crystal ( 14.7456MHZ.32.768KHZ)

• Relay driver (ULN2803)

• Regulator 3.3V (LMS8 1 I 7A or MIC5209)

• Regulator 1 .8V (LMS81 17 A or MIC5209)

• Battery (3.6 V,60m A)

• Relay ( 12/6A)

• Opto-Couplers(PC8 l 7)

• Transistor(BC547, BC556 ) Energy Meter Module:

• Energy measuring ASIC (AD7758SSOP)

• Isolators (AD140 ) , PC81 7)

• TT L AND gate IC(74HC08)

• Reference Voltage 1C (ADR421 BR)

• Crystal ( 1 OMHZ)

Features of main board

1 . 32 bit ARM controller based mother board.

2. I EC l O I , I EC- 104, DN P3, or Modbus protocol support to communicate with master.

3. 2 Serial ports(RS232/RS485) to communicate with Configuration Util ity and master

4. Master com' port uses CTS and RTS signals with preamble & post amble.

5. RTS watch dog.

6. H igh accuracy RTC

7. Master commun ication port baud rates are configurable with jumper settings.

8. External memory of 32K is provided, can be expandable up to 64MB to store the events and instant parameters.

9. Communicates with the meter module using SPI bus. The parameters that it can store are as follows:

1 . R, Y, B phase voltages.

2. R, Y, B phase currents.

3. Power Factor R, Y, B.

4. Total PF.

5. Total Active power KW.

6. Total Reactive Power KVAR.

7. Total Apparent Power KVA.

8. Max Demand KVA l 5Min.

9. Max Demand KVA 30M in.

10. Last average demand KVA l iMin.

1 1 . Last average demand KVA 30M in.

12. Total Active Energy KWH (Import).

13. Total Active Energy KWH (Export).

14. Total Reactive Energy Lead KVARH.

15. Total Reactive Energy lag KVARH .

• 4No. Digital outputs with 5 Relays (Potential free contacts).

• 8No. of Digital inputs (optical isolated).

• LED indications to display Relays and Digital inputs status.

• Communication DSP based meter module using SPI interface.

• SPI speed is 460KHZ.

• 12C speed is 400KHZ.

Circuit Description

• The main controller in the CPU module is LPC22 14 ARM controller in which we are using 2 serial ports and an SPI port.

• 2 serial ports UARTO and UARTI

• UARTO is used for programming of microcontroller using ISP.

• In our circuit, UARTO is used for programming firmware and to communicate with configuration/Debug utility.

• UARTI is for communication with master station. This has hardware handshaking also.

• In UARTO and UARTI max232 ICs are used.

• Two RTC s are present. One is PCF8563 and other one is RX8025 (Epson RTC). RX8025 is the most accurate (+/- 5 PPM). Since this is not readily available in local market, DS 1302 also used for stand-by. The PCF8563 communicates with controller with general purpose IO pins where as Epson RTC uses I2C pins.

• A 32 Pin NV RAM (32K) is used in the mother board.

• With LM35 on board temperature can be monitored. This is semiconductor temperature sensor. It gives out put which linearly proportional to temperature ( l OmVolt/ Deg' C).

• SPI interface is used to communicate with meter board

• LDO regulators are used to convert 5.6V DC power supply to 3.6V and 1 .8V.

• The RTS pin of 2214 (UART l ) is controlled by RTS watch dog if it is kept low for more than I Osec

• Baud rate can be 4800, 9600 and 19200. RTS Preamble time can be 50 ms, 100ms , 150ms and 200ms.

• Whether the Unit is running on Mains or battery input can be monitored via

mains and battery input pin (Ref connector description of J23) The battery voltage can also be monitored.

• Watch dog (DS 1232) is used to reset the controller if it hangs.

• LED indications are provided for power supply (5v. 3.3v and l .8v), UART l RX, TX, RTS, CTS pins, CPU health check and Watch dog reset.

• JTAG connecter is provided for debugging.

• LM81 1 7-3.3(LSO I ) and LM8 I 1 7- 1 .8 (LSOO) regulators to convert power supply 5v to 3.3v and 1 ,8v respective

• DS 1232 IC using as external watchdog timer. DS I 232 monitors software execution every 250msec.

• U LN2003A has high voltage, high current Darlington arrays. This device is for driving relays.

• Read digital input status every 10m sec PCl 87 opt couplers provide isolation between controller and digital inputs.

Bill of Materials

Table 1

S. No [Part Reference ^" Part Number Part Description IM anufacturer

LED's Description

Table 3

Test Point Identification:

Table 4

CONNECTOR CONFIGURATION

CONNECTOR J6: POWER SUPPLY INPUT

Table 5

CONNECTOR Jl :

SERIAL PORT CONNECTOR (UARTl):

Table 5 1

CONNECTOR J4: Connector for Digital Inputs

Table 5 2

CONNECTOR J3: Digital Output Connector:

Table: 5 3

CONNECTOR J5A:

RMC Connector to Meter Module:

Table 5 4

Module-2: METER MODULE

Introduction

The ADE7758 is a high accuracy 3-phase electrical energy measurement with a serial interface and two pulse outputs The ADE77S8 incorpoi ates second-order sigma-delta ADCs a digital integrator, reference circuitry, temperature sensor, and all the signal processing required to perform active, reactive and apparent energy measurement and rnu calculations T his module is interfaced with the main board through SPI interface

Features

• High accuiac), supports IEC 60687, IEC 61036, IEC 61268, IEC 62053-21,

IKC 62053-22. and i EC 62053-23.

• Compatible with 3-phase/3-wire, 3-phase/4-wιre, and other 3-phase services.

• Less than 0.1 % active energy error over a dynamic range of 1000 to I at 25 ⁰ C

• Supplies active/reactive/apparent energy, voltage RMS, current RMS, and sampled waveform data.

• Two pulse outputs, one for active power and the other selectable between reactive and apparent power with programmable frequency

• Digital power, phase, and RMS offset calibration

• On-chip user programmable thresholds for line voltage SAG and over voltage detections

• On-chip digital integrator enables direct interface-to-current sensors with di/dt output

• A PGA in the current channel allows direct interface to shunts and current transformers

• A SPI compatible serial interface with IRQ.

• Reference 2.4 V (drift 30 ppm/°C typ) with external overdrive capability Single 5 V supply, low power (70 niW typ)

Circuit Description

ANALOG INPUTS

Refer fig 6.1 b Schematic of Voltage signals arc connected to J l with screw terminals. CTs are mounted υn PCB. All analog input signals are filtered using the nn-board anti-alias filters before being presented to (he analog inputs of the ADF.7758.

CURRENT SENSE INPUTS (J2, J4 AND J5)

Refer the fig 6.1 c schematic of meter module. .12, J4 and J5 are two-w;iy connection blocks which allow ADE7758's current inputs of phase A, B and C respectively to be

connected to current transducers. The position is given to mount CTs on PCB directly. Schematic shows the connector J2 and the filtering network which is provided on the meter board. The resistors R I O. R20 are to be used as burden resistors when CTs are used as the current transducers. The RC networks R7/C3, R 16/C5, R22/C8, R35/C 12. R41 /C 16, R49/C20 arc used to provide phase compensation when a Current Transformer is being used as the current transducer with the ADB7758.The RC networks R l /C l . R2/C2, R 1 5/C7 and R30/C I 1 are the anti-alias filters which are required by the on-chip ADCs. The default corner frequency for these LPFs (Low Pass Filters) is selected as 4.8 kHz ( l kω& 33nF).

VOLTAG E SENSE INPUTS (.31 )

Refer the fig 6.1 b Schematic of meter module. The voltage inputs connections on the ADH7758 meter board can be directly connected to the line voltage sources. The line voltages are attenuated tising a simple resistor divider network before it is presented to the ADR7758. The attenuation network on the voltage channels is designed such ihat the coi ner frequency (3dEJ frequency) of the network matches that ^' of the RC (anti-aliasing) filters on the current channels inputs. This is important, because if they do not match there will be large errors at low power factors. The Serial interface along with the digital parameters of the ADE7758 enable a ful ly software calibration procedure. In this case, the voltage attenuation networks are made up of R2. R3 and R5 for Phase A, R 14, R 1 5. R 19 for Phase B and R29, R30 and R34 for Phase C. Schematic shows typical connection for the line voltage when using fixed resistors.

6.2.6 SPECIFICATIONS

Table: 6

Bill of Materials

Table. I

LED's Description :

Table 8

Test Point Identification:

Table. 9

CONNECTOR CONFIGURATION

CONNECTOR J6: POWER SUPPLY

Table IO 1

CONNECTOR Jl: 3 PHASE SUPPLY

Table 102

Terminal connector

Form C Connectors:

1 ) A cable come from Form C I B make I turns (enter from arrow mark) to CTl on meter board and goes to Form C 3B.

Form C I A to Form C 2A short. Form C 2B to Form C 3A short.

2) Same as 1 . Form C 4B - CT2 - Form C 6B.

Form C 4A to Form C 5A short. Form C 5B to Form C 6A short.

3) Same as I . Form C 7B - CT3 - Form C 9B.

Form C 7A to Form C 8A short. Form C 8B to Form C 9A short.

Note: Form C xA input side. Form C xB meter module side Note: Ring type Lugs to be used for all Form C connections.

MCB connections:

1 ) Neural 2) B phase 3) Y Phase 4) R Phase

To Power supply and meter module with twisted cables.