ANSI codes for Protection Functions

The ANSI(American National Standards Institute) has standardized the codes to be used for protection relays. Each protective function is indicated by a specific no. such as 50 for instantaneous overcurrent protection and 59 for overvoltage protection.

Following is the list of the functions. The codes are sometimes followed by an alphabet which gives some additional information for instance, the code 51G may indicate an overcurrent ground relay. 50N may indicate a ground sensitive overcurrent relay based on neutral current measurement. 87T may indicate that a differential relay may be used for Transformer protection.

1 - Master Element
2 - Time Delay Starting or Closing Relay
3 - Checking or Interlocking Relay
4 - Master Contactor
5 - Stopping Device
6 - Starting Circuit Breaker
7 - Anode Circuit Breaker
8 - Control Power Disconnecting Device
9 - Reversing Device
10 - Unit Sequence Switch
11 - Reserved for future application
12 - Overspeed Device
13 - Synchronous-speed Device
14 - Underspeed Device
15 - Speed - or Frequency, Matching Device
16 - Reserved for future application
17 - Shunting or Discharge Switch
18 - Accelerating or Decelerating Device
19 - Starting to Running Transition Contactor
20 - Electrically Operated Valve
21 - Distance Relay
22 - Equalizer Circuit Breaker
23 - Temperature Control Device
24 - Over-Excitation Relay (V/Hz)
25 - Synchronizing or Synchronism-Check Device
26 - Apparatus Thermal Device
27 - Undervoltage Relay
28 - Flame Detector
29 - Isolating Contactor
30 - Annunciator Relay
31 - Separate Excitation Device
32 - Directional Power Relay
33 - Position Switch
34 - Master Sequence Device
35 - Brush-Operating or Slip-Ring Short-Circuiting, Device
36 - Polarity or Polarizing Voltage Devices
37 - Undercurrent or Underpower Relay
38 - Bearing Protective Device
39 - Mechanical Conduction Monitor
40 - Field Relay
41 - Field Circuit Breaker
42 - Running Circuit Breaker
43 - Manual Transfer or Selector Device
44 - Unit Sequence Starting Relay
45 - Atmospheric Condition Monitor
46 - Reverse-phase or Phase-Balance Current Relay
47 - Phase-Sequence Voltage Relay
48 - Incomplete Sequence Relay
49 - Machine or Transformer, Thermal Relay
50 - Instantaneous Overcurrent or Rate of Rise, Relay 51 - AC Time Overcurrent Relay 52 - AC Circuit Breaker 53 - Exciter or DC Generator Relay 54 - High-Speed DC Circuit Breaker 55 - Power Factor Relay 56 - Field Application Relay 57 - Short-Circuiting or Grounding (Earthing) Device 58 - Rectification Failure Relay 59 - Overvoltage Relay 60 - Voltage or Current Balance Relay 61 - Machine Split Phase Current Balance 62 - Time-Delay Stopping or Opening Relay 63 - Pressure Switch 64 - Ground (Earth) Detector Relay 65 - Governor 66 - Notching or Jogging Device 67 - AC Directional Overcurrent Relay 68 - Blocking Relay 69 - Permissive Control Device 70 - Rheostat 71 - Level Switch 72 - DC Circuit Breaker 73 - Load-Resistor Contactor 74 - Alarm Relay 75 - Position Changing Mechanism 76 - DC Overcurrent Relay 77 - Pulse Transmitter 78 - Phase-Angle Measuring or Out-of-Step Protective Relay 79 - AC Reclosing Relay 80 - Flow Switch 81 - Frequency Relay 82 - DC Reclosing Relay 83 - Automatic Selective Control or Transfer Relay 84 - Operating Mechanism 85 - Carrier or Pilot-Wire Receiver Relay 86 - Lockout Relay 87 - Differential Protective Relay 88 - Auxiliary Motor or Motor Generator 89 - Line Switch 90 - Regulating Device 91 - Voltage Directional Relay 92 - Voltage and Power Directional Relay 93 - Field Changing Contactor 94 - Tripping or Trip-Free Relay 95 - Reluctance Torque Synchrocheck 96 - Autoloading Relay

Breakdown in Liquids due to the presence of suspended particles

In commercial liquids, which are not pure, the presence of suspended foreign particles has a significant impact on the overall breakdown strength.

When an electric field is applied across such a commercial liquid, the suspended particles align themselves depending on their permittivities.  If the permittivity of the suspended particles is more than the liquid, eg. paper particles, the particle will experience a force towards the area of higher stress.

If the permittivity of the particle is lesser than that of the liquid, eg. gas bubbles, the particle will experience a force towards the area of lower stress.

This results in the particles aligning themselves in a region.  As they accumulate, they may bridge the two electrodes and cause a breakdown.

Liquid Dielectrics

Liquid Dielectrics find wide application as insulating materials in electric equipment such as transformers, cables and switchgear.  In Transformers, insulating oils are used to provide insulation to the live parts and to transfer heat away from the hot regions.  In Circuit breakers, oil is used to extinguish the arc which occurs when the breaker opens.

Any change in the insulating properties of these dielectrics can cause damage to the equipment and result in breakdowns.  Hence, it is necessary to have a good understanding of the insulating properties of dielectrics.

From an Electrical perspective, the main properties of the insulating oil are the dielectric constant, the dielectric strength and the electrical conductivity.  

The purity of the insulating liquid is vital.  Even a small amount of water, say 0.01% can reduce the dielectric strength of oil by 20%.  The presence of other impurities can also reduce the dielectric strength sharply.  

From the perspective of insulation, liquids are classified into pure liquids and commercial liquids.  Pure liquids are those in which the amount of impurities are less than 1 in 10^9.  

Commercial liquids, on the other hand, are impure liquids which contain impurities such water, other chemical molecules and foreign particles.  These liquids are not homogeneous.  It is common to find that two samples taken from the same transformer having different properties.