pythonからpostgres int型のカラムにnull値を格納したい

pythonのpsycopg2ライブラリを使用して、int型とtimestamp型のカラムにnull値を入れようとすると下記エラー
が発生します。

【エラー内容】
psycopg2.DataError: invalid input syntax for type timestamp: "None"
LINE 1: ...'?$filter=id%20eq%20174556','uno','1','V12102629','None','Ou...

エラーが発生している変数には下記のようにNoneを代入しています。
clearance_time_at = None

エラーが発生しないようにnullを格納する方法をご教示お願いします。

-----エラーが発生しているコード------------

         if alarm.get('vpnGroupId'):
            vpn_group_id = alarm['vpnGroupId']
         else:
            alarm['vpnGroupId'] = None
            vpn_group_id = alarm['vpnGroupId']

         customer_id = alarm['customerId']

         if alarm.get('clearanceTime'):
            clearance_time_at = alarm['clearanceTime']
         else:
            clearance_time_at = None　　　#エラーが発生している変数

         state = alarm['state']
         managed_object = alarm['managedObject']
         probable_cause = alarm['probableCause']
         specific_problems = alarm['specificProblems']
         creation_time_at = alarm['creationTime']　　#以下変数省略・・・
query_alarms = "INSERT INTO alarms(alarm_id,element,customer_system,planned_maintenance,customer_planned_maintenance,first_content,\
                                            latest_content,first_severity,latest_severity,identifier,href,service_name,process_type,\
                                            vpn_group_id,clearance_time_at,state,managed_object,probable_cause,specific_problems,creation_time_at,\
                                            last_modification_time_at,equipment_pattern,root_cause_pattern,user_cause_judge_reason,\
                                            root_cause_description_jp,root_cause_description_en,request_description_jp,request_description_en,\
                                            ticket_id,problem_alarm,sub_alarm,first_occurrence_at,last_occurrence_at,created_at,created_by,\
                                            last_update_at,last_update_by,data_virtualizer,data_virtualizer_pkey,is_active\
                                            ,alarm_description_jp,alarm_description_en,is_root_cause,item_code,object_code)\
                        VALUES ('%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s',\
                                '%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s','%s')\
                        ON CONFLICT ON CONSTRAINT alarms_alarm_id_key \
                        DO UPDATE SET element='%s',customer_system='%s',planned_maintenance='%s',customer_planned_maintenance='%s',\
                        first_content='%s',latest_content='%s', first_severity='%s', latest_severity='%s', identifier='%s',\
                        href='%s', service_name='%s',process_type='%s', vpn_group_id='%s', customer_id='%s',\
                        clearance_time_at='%s', state='%s', managed_object='%s', probable_cause='%s',specific_problems='%s',\
                        creation_time_at='%s', last_modification_time_at='%s',equipment_pattern='%s', root_cause_pattern='%s', user_cause_judge_reason='%s',\
                        root_cause_description_jp='%s', root_cause_description_en='%s', request_description_jp='%s', request_description_en='%s',ticket_id='%s',\
                        problem_alarm='%s', sub_alarm='%s',first_occurrence_at='%s', last_occurrence_at='%s', last_update_at='%s',\
                        last_update_by='%s', data_virtualizer='%s',is_active='%s',alarm_description_jp='%s', alarm_description_en='%s',\
                        is_root_cause ='%s',item_code = '%s',object_code='%s'"


         cursor.execute(query_alarms % (alarm_id, element, customer_system, planned_maintenance, customer_planned_maintenance, first_content,
                                       latest_content, first_severity, latest_severity, identifier, href, service_name, process_type,
                                       vpn_group_id, clearance_time_at, state, managed_object, probable_cause, specific_problems, creation_time_at,
                                       last_modification_time_at, equipment_pattern, root_cause_pattern, user_cause_judge_reason, root_cause_description_jp,
                                       root_cause_description_en, request_description_jp, request_description_en, ticket_id, problem_alarm, sub_alarm,
                                       first_occurrence_at, last_occurrence_at, created_at, created_by, last_update_at, last_update_by, data_virtualizer,
                                       data_virtualizer_pkey, is_active, alarm_description_jp, alarm_description_en, is_root_cause, item_code, object_code,
                                       element, customer_system, planned_maintenance, customer_planned_maintenance,
                                       first_content, latest_content, first_severity, latest_severity, identifier,
                                       href, service_name, process_type, vpn_group_id, customer_id,
                                       clearance_time_at, state, managed_object, probable_cause, specific_problems,
                                       creation_time_at, last_modification_time_at, equipment_pattern, root_cause_pattern, user_cause_judge_reason,
                                       root_cause_description_jp, root_cause_description_en, request_description_jp, request_description_en, ticket_id,
                                       problem_alarm, sub_alarm, first_occurrence_at, last_occurrence_at, last_update_at,
                                       last_update_by, data_virtualizer, is_active, alarm_description_jp, alarm_description_en, is_root_cause, item_code, object_code))